diff --git a/Modules/Invoices/Peppol/FormatHandlers/EhfHandler.php b/Modules/Invoices/Peppol/FormatHandlers/EhfHandler.php
index 2260d494..d9ebe294 100644
--- a/Modules/Invoices/Peppol/FormatHandlers/EhfHandler.php
+++ b/Modules/Invoices/Peppol/FormatHandlers/EhfHandler.php
@@ -17,7 +17,7 @@
 class EhfHandler extends BaseFormatHandler
 {
     /**
-     * Constructor.
+     * Initialize the handler and set the Peppol document format to EHF.
      */
     public function __construct()
     {
@@ -25,7 +25,11 @@ public function __construct()
     }
 
     /**
-     * {@inheritdoc}
+     * Builds a Peppol EHF-compliant invoice payload as an associative array from the given Invoice.
+     *
+     * @param Invoice $invoice The invoice model used to populate the payload.
+     * @param array $options Optional transform options (reserved for future use).
+     * @return array An associative array representing the EHF/Peppol invoice with top-level keys such as `ubl_version_id`, `customization_id`, `profile_id`, `id`, `issue_date`, `due_date`, `invoice_type_code`, `document_currency_code`, `buyer_reference`, `accounting_supplier_party`, `accounting_customer_party`, `delivery`, `payment_means`, `payment_terms`, `tax_total`, `legal_monetary_total`, and `invoice_line`.
      */
     public function transform(Invoice $invoice, array $options = []): array
     {
@@ -71,11 +75,15 @@ public function transform(Invoice $invoice, array $options = []): array
     }
 
     /**
-     * Build supplier party.
+     * Builds the supplier party structure for the EHF (Peppol) invoice payload.
+     *
+     * Returns a nested array under the `party` key containing the supplier's Peppol endpoint ID, party identification
+     * (organization number), company name, postal address (street, city, postal zone, country), tax scheme (VAT),
+     * legal entity details (registration name and address) and contact details (name, phone, email).
      *
-     * @param Invoice $invoice
-     * @param mixed $endpointScheme
-     * @return array<string, mixed>
+     * @param Invoice $invoice Invoice model (source of contextual invoice data; supplier values are taken from config).
+     * @param mixed $endpointScheme Enum-like object providing the Peppol endpoint scheme identifier via `$endpointScheme->value`.
+     * @return array<string,mixed> Structured supplier party data for inclusion in the transformed EHF payload.
      */
     protected function buildSupplierParty(Invoice $invoice, $endpointScheme): array
     {
@@ -131,11 +139,14 @@ protected function buildSupplierParty(Invoice $invoice, $endpointScheme): array
     }
 
     /**
-     * Build customer party.
+     * Constructs the customer party section for an EHF invoice payload.
      *
-     * @param Invoice $invoice
-     * @param mixed $endpointScheme
-     * @return array<string, mixed>
+     * @param Invoice $invoice Invoice containing customer data used to populate party fields.
+     * @param mixed $endpointScheme Object providing a `value` property used as the endpoint identification scheme.
+     * @return array<string,mixed> Array representing the customer party with keys: `party` => [
+     *     'endpoint_id', 'party_identification', 'party_name', 'postal_address',
+     *     'party_legal_entity', 'contact'
+     * ].
      */
     protected function buildCustomerParty(Invoice $invoice, $endpointScheme): array
     {
@@ -182,11 +193,13 @@ protected function buildCustomerParty(Invoice $invoice, $endpointScheme): array
     }
 
     /**
-     * Build delivery information.
-     *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
-     */
+         * Constructs the delivery information array using the invoice date and the customer's address.
+         *
+         * @param Invoice $invoice The invoice from which to derive the delivery date and customer address.
+         * @return array<string,mixed> Array with keys:
+         *                             - `actual_delivery_date`: date string in `YYYY-MM-DD` format,
+         *                             - `delivery_location`: array containing `address` with `street_name`, `city_name`, `postal_zone`, and `country` (`identification_code`).
+         */
     protected function buildDelivery(Invoice $invoice): array
     {
         return [
@@ -205,11 +218,17 @@ protected function buildDelivery(Invoice $invoice): array
     }
 
     /**
-     * Build payment means.
-     *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
-     */
+         * Builds the payment means section for the given invoice.
+         *
+         * @param Invoice $invoice Invoice used to populate the payment identifier (`payment_id`).
+         * @return array<string, mixed> An associative array containing:
+         *                              - `payment_means_code`: code representing the payment method (credit transfer).
+         *                              - `payment_id`: invoice number used as the payment identifier.
+         *                              - `payee_financial_account`: account information with keys:
+         *                                  - `id`: supplier bank account number,
+         *                                  - `name`: supplier company name,
+         *                                  - `financial_institution_branch`: bank branch info with `id` (BIC) and `name` (bank name).
+         */
     protected function buildPaymentMeans(Invoice $invoice): array
     {
         return [
@@ -227,10 +246,10 @@ protected function buildPaymentMeans(Invoice $invoice): array
     }
 
     /**
-     * Build payment terms.
+     * Constructs payment terms with a Norwegian note stating the number of days until the invoice is due.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice used to calculate days until due.
+     * @return array<string, mixed> An array containing a 'note' key with value like "Forfall X dager" where X is the number of days until due.
      */
     protected function buildPaymentTerms(Invoice $invoice): array
     {
@@ -242,12 +261,19 @@ protected function buildPaymentTerms(Invoice $invoice): array
     }
 
     /**
-     * Build tax total.
-     *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<string, mixed>
-     */
+         * Constructs the invoice tax total including per-rate subtotals.
+         *
+         * Builds the overall tax amount and an array of tax subtotals grouped by tax rate;
+         * each subtotal contains the taxable amount, tax amount (both formatted with the provided currency),
+         * and a tax category (id, percent and tax scheme).
+         *
+         * @param Invoice $invoice The invoice to compute taxes for.
+         * @param string $currencyCode ISO 4217 currency code used for all monetary values.
+         * @return array<string,mixed> An array with keys:
+         *                             - `tax_amount`: array with `value` and `currency_id` for the total tax,
+         *                             - `tax_subtotal`: list of per-rate subtotals each containing `taxable_amount`,
+         *                               `tax_amount`, and `tax_category`.
+         */
     protected function buildTaxTotal(Invoice $invoice, string $currencyCode): array
     {
         $taxAmount = $invoice->invoice_total - $invoice->invoice_subtotal;
@@ -301,11 +327,15 @@ protected function buildTaxTotal(Invoice $invoice, string $currencyCode): array
     }
 
     /**
-     * Build monetary total.
+     * Construct the invoice monetary totals section for the EHF payload.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<string, mixed>
+     * @param Invoice $invoice Invoice model containing subtotal and total amounts.
+     * @param string $currencyCode ISO 4217 currency code used for all monetary values.
+     * @return array<string, mixed> Associative array with these keys:
+     *     - `line_extension_amount`: array with `value` (amount before taxes as a string with two decimals) and `currency_id`.
+     *     - `tax_exclusive_amount`: array with `value` (amount excluding tax as a string with two decimals) and `currency_id`.
+     *     - `tax_inclusive_amount`: array with `value` (amount including tax as a string with two decimals) and `currency_id`.
+     *     - `payable_amount`: array with `value` (final payable amount as a string with two decimals) and `currency_id`.
      */
     protected function buildMonetaryTotal(Invoice $invoice, string $currencyCode): array
     {
@@ -330,11 +360,15 @@ protected function buildMonetaryTotal(Invoice $invoice, string $currencyCode): a
     }
 
     /**
-     * Build invoice lines.
+     * Create an array of invoice line entries for the EHF Peppol document.
+     *
+     * Each entry corresponds to an invoice item and includes identifiers, quantity,
+     * line extension amount, item details (description, name, seller item id, tax
+     * classification) and price information.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<int, array<string, mixed>>
+     * @param Invoice $invoice Invoice model containing `invoiceItems` to convert into lines.
+     * @param string $currencyCode ISO 4217 currency code applied to monetary fields.
+     * @return array<int, array<string, mixed>> Array of invoice line structures ready for transformation. 
      */
     protected function buildInvoiceLines(Invoice $invoice, string $currencyCode): array
     {
@@ -380,7 +414,15 @@ protected function buildInvoiceLines(Invoice $invoice, string $currencyCode): ar
     }
 
     /**
-     * {@inheritdoc}
+     * Generate the EHF-formatted document for an invoice as a string.
+     *
+     * Converts the given Invoice into the EHF document representation and returns it
+     * as a string. Note: the current implementation returns a JSON-encoded
+     * representation of the transformed data as a placeholder for the final XML.
+     *
+     * @param Invoice $invoice The invoice to convert.
+     * @param array $options Optional transformation options.
+     * @return string The EHF-formatted document as a string; currently a JSON-encoded representation of the transformed data (placeholder for proper XML).
      */
     public function generateXml(Invoice $invoice, array $options = []): string
     {
@@ -391,8 +433,13 @@ public function generateXml(Invoice $invoice, array $options = []): string
     }
 
     /**
-     * {@inheritdoc}
-     */
+         * Validate invoice fields required by the EHF (Norwegian Peppol) format.
+         *
+         * Performs format-specific checks and returns any validation error messages.
+         *
+         * @param Invoice $invoice The invoice to validate.
+         * @return string[] An array of validation error messages; empty if the invoice meets EHF requirements.
+         */
     protected function validateFormatSpecific(Invoice $invoice): array
     {
         $errors = [];
@@ -411,10 +458,10 @@ protected function validateFormatSpecific(Invoice $invoice): array
     }
 
     /**
-     * Get buyer reference.
+     * Selects the buyer reference used for EHF routing.
      *
-     * @param Invoice $invoice
-     * @return string
+     * @param Invoice $invoice Invoice to extract the buyer reference from.
+     * @return string The buyer reference from the invoice's customer if present, otherwise the invoice reference, or an empty string if neither is set.
      */
     protected function getBuyerReference(Invoice $invoice): string
     {
@@ -423,13 +470,13 @@ protected function getBuyerReference(Invoice $invoice): string
     }
 
     /**
-     * Get tax rate from invoice item.
-     *
-     * @param mixed $item
-     * @return float
-     */
+         * Return the tax rate percentage for an invoice item.
+         *
+         * @param mixed $item Invoice item (object or array) that may contain a `tax_rate` value.
+         * @return float The tax rate as a percentage (e.g., 25.0). Defaults to 25.0 when not present.
+         */
     protected function getTaxRate($item): float
     {
         return $item->tax_rate ?? 25.0; // Standard Norwegian VAT rate
     }
-}
+}
\ No newline at end of file
diff --git a/Modules/Invoices/Peppol/FormatHandlers/FacturXHandler.php b/Modules/Invoices/Peppol/FormatHandlers/FacturXHandler.php
index 17f26ae9..fc09d8cb 100644
--- a/Modules/Invoices/Peppol/FormatHandlers/FacturXHandler.php
+++ b/Modules/Invoices/Peppol/FormatHandlers/FacturXHandler.php
@@ -17,7 +17,9 @@
 class FacturXHandler extends BaseFormatHandler
 {
     /**
-     * Constructor.
+     * Initialize the handler for the Factur-X 1.0 (Cross Industry Invoice) Peppol document format.
+     *
+     * Sets the format identifier to PeppolDocumentFormat::FACTURX_10 via the parent constructor.
      */
     public function __construct()
     {
@@ -34,11 +36,11 @@ public function transform(Invoice $invoice, array $options = []): array
     }
 
     /**
-     * Build CII structure for Factur-X.
-     *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
-     */
+         * Constructs the Cross Industry Invoice (CII) array representation for a Factur‑X 1.0 invoice.
+         *
+         * @param Invoice $invoice The invoice to convert into the CII structure.
+         * @return array<string, mixed> An associative array representing the CII payload with the root key `rsm:CrossIndustryInvoice`.
+         */
     protected function buildCiiStructure(Invoice $invoice): array
     {
         $customer = $invoice->customer;
@@ -57,9 +59,9 @@ protected function buildCiiStructure(Invoice $invoice): array
     }
 
     /**
-     * Build document context section.
+     * Constructs the document context parameters required by the Factur‑X (CII) envelope.
      *
-     * @return array<string, mixed>
+     * @return array<string, mixed> Array containing `ram:GuidelineSpecifiedDocumentContextParameter` with `ram:ID` set to the Factur‑X guideline URN.
      */
     protected function buildDocumentContext(): array
     {
@@ -71,10 +73,13 @@ protected function buildDocumentContext(): array
     }
 
     /**
-     * Build exchanged document section.
+     * Builds the ExchangedDocument section of the CII (Factur‑X) payload for the given invoice.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice whose identifying and date information will populate the section.
+     * @return array<string,mixed> Associative array with keys:
+     *                              - `ram:ID`: invoice number,
+     *                              - `ram:TypeCode`: document type code ('380' for commercial invoice),
+     *                              - `ram:IssueDateTime`: contains `udt:DateTimeString` with `@format` '102' and the invoice date formatted as `Ymd`.
      */
     protected function buildExchangedDocument(Invoice $invoice): array
     {
@@ -91,11 +96,11 @@ protected function buildExchangedDocument(Invoice $invoice): array
     }
 
     /**
-     * Build supply chain trade transaction section.
+     * Builds the Supply Chain Trade Transaction section of the CII payload.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice to extract trade data from.
+     * @param string $currencyCode ISO 4217 currency code used for monetary elements.
+     * @return array<string,mixed> Array containing keys for 'ram:ApplicableHeaderTradeAgreement', 'ram:ApplicableHeaderTradeDelivery', and 'ram:ApplicableHeaderTradeSettlement' representing their respective CII subsections.
      */
     protected function buildSupplyChainTradeTransaction(Invoice $invoice, string $currencyCode): array
     {
@@ -107,10 +112,13 @@ protected function buildSupplyChainTradeTransaction(Invoice $invoice, string $cu
     }
 
     /**
-     * Build header trade agreement section.
+     * Constructs seller and buyer party data for the CII header trade agreement.
+     *
+     * Seller values are sourced from configuration; buyer values are populated from the
+     * invoice's customer (company/name and postal address).
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice whose customer and address data populate the buyer party.
+     * @return array<string,mixed> An array containing `ram:SellerTradeParty` and `ram:BuyerTradeParty` structures suitable for the CII header trade agreement.
      */
     protected function buildHeaderTradeAgreement(Invoice $invoice): array
     {
@@ -145,10 +153,10 @@ protected function buildHeaderTradeAgreement(Invoice $invoice): array
     }
 
     /**
-     * Build header trade delivery section.
+     * Builds the header trade delivery section containing the actual delivery event date.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * @param Invoice $invoice Invoice model whose invoiced_at date is used for the delivery occurrence.
+     * @return array<string, mixed> Array representing `ram:ActualDeliverySupplyChainEvent` with `ram:OccurrenceDateTime` containing a `udt:DateTimeString` using format '102' and the invoice date formatted as `Ymd`.
      */
     protected function buildHeaderTradeDelivery(Invoice $invoice): array
     {
@@ -165,11 +173,10 @@ protected function buildHeaderTradeDelivery(Invoice $invoice): array
     }
 
     /**
-     * Build header trade settlement section.
+     * Construct the header trade settlement block for the invoice's CII payload, including currency, payment means, tax totals, payment terms, monetary summation, and line items.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<string, mixed>
+     * @param string $currencyCode ISO 4217 currency code used for monetary amounts.
+     * @return array<string, mixed> The `ram:ApplicableHeaderTradeSettlement` structure ready for inclusion in the CII document.
      */
     protected function buildHeaderTradeSettlement(Invoice $invoice, string $currencyCode): array
     {
@@ -202,12 +209,16 @@ protected function buildHeaderTradeSettlement(Invoice $invoice, string $currency
     }
 
     /**
-     * Build tax totals.
-     *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<array<string, mixed>>
-     */
+         * Aggregate invoice item taxes by tax rate and format them for the CII tax totals section.
+         *
+         * Each returned entry represents a tax group for a specific rate and includes the calculated tax amount,
+         * the taxable basis, the VAT category code, and the applicable rate percent. Monetary and percent values
+         * are formatted as strings with two decimal places and a dot decimal separator.
+         *
+         * @param Invoice $invoice The invoice whose items will be grouped by tax rate.
+         * @param string $currencyCode ISO 4217 currency code used for the tax totals (included for context).
+         * @return array<int, array<string, mixed>> Array of tax entries suitable for embedding under `ram:ApplicableTradeTax`.
+         */
     protected function buildTaxTotals(Invoice $invoice, string $currencyCode): array
     {
         // Group items by tax rate
@@ -243,11 +254,14 @@ protected function buildTaxTotals(Invoice $invoice, string $currencyCode): array
     }
 
     /**
-     * Build line items.
+     * Constructs the CII-formatted line items for the given invoice.
+     *
+     * Each entry contains product details, net price, billed quantity (with unit code),
+     * applicable tax information, and the line total amount formatted for Factur‑X CII.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<array<string, mixed>>
+     * @param Invoice $invoice The invoice containing items to convert.
+     * @param string $currencyCode ISO 4217 currency code used for monetary formatting.
+     * @return array<int, array<string, mixed>> Array of associative arrays representing CII line-item entries.
      */
     protected function buildLineItems(Invoice $invoice, string $currencyCode): array
     {
@@ -288,7 +302,11 @@ protected function buildLineItems(Invoice $invoice, string $currencyCode): array
     }
 
     /**
-     * {@inheritdoc}
+     * Generate the Factur‑X (CII) representation for an invoice and, in a full implementation, embed it into a PDF/A‑3 container.
+     *
+     * @param Invoice $invoice The invoice to convert into Factur‑X (CII) format.
+     * @param array $options Optional generation options that may alter output formatting or embedding behavior.
+     * @return string The generated output. Currently returns a pretty-printed JSON string of the internal CII structure (placeholder for the eventual PDF/A‑3 with embedded XML).
      */
     public function generateXml(Invoice $invoice, array $options = []): string
     {
@@ -303,7 +321,12 @@ public function generateXml(Invoice $invoice, array $options = []): string
     }
 
     /**
-     * {@inheritdoc}
+     * Validate format-specific requirements for Factur-X invoices.
+     *
+     * Ensures the invoice meets constraints required by the Factur-X (CII) format.
+     *
+     * @param Invoice $invoice The invoice to validate.
+     * @return string[] An array of validation error messages; empty if there are no format-specific errors.
      */
     protected function validateFormatSpecific(Invoice $invoice): array
     {
@@ -318,13 +341,13 @@ protected function validateFormatSpecific(Invoice $invoice): array
     }
 
     /**
-     * Get tax rate from invoice item.
-     *
-     * @param mixed $item
-     * @return float
-     */
+         * Retrieve the tax rate percentage for an invoice item.
+         *
+         * @param mixed $item Invoice item (object or array) that may provide a `tax_rate` property or key.
+         * @return float The tax rate percentage for the item; defaults to 20.0 if not present.
+         */
     protected function getTaxRate($item): float
     {
         return $item->tax_rate ?? 20.0; // Default French VAT rate
     }
-}
+}
\ No newline at end of file
diff --git a/Modules/Invoices/Peppol/FormatHandlers/FacturaeHandler.php b/Modules/Invoices/Peppol/FormatHandlers/FacturaeHandler.php
index c67d475b..d8c86a96 100644
--- a/Modules/Invoices/Peppol/FormatHandlers/FacturaeHandler.php
+++ b/Modules/Invoices/Peppol/FormatHandlers/FacturaeHandler.php
@@ -17,7 +17,7 @@
 class FacturaeHandler extends BaseFormatHandler
 {
     /**
-     * Constructor.
+     * Initialize the handler and register the Facturae 3.2 document format.
      */
     public function __construct()
     {
@@ -25,7 +25,14 @@ public function __construct()
     }
 
     /**
-     * {@inheritdoc}
+     * Transform an Invoice model into a Facturae 3.2 structured array payload.
+     *
+     * Builds the top-level Facturae structure containing `FileHeader`, `Parties` and `Invoices`
+     * suitable for downstream encoding to the Facturae 3.2 representation.
+     *
+     * @param Invoice $invoice The invoice to transform.
+     * @param array $options Optional transformation options.
+     * @return array The Facturae-structured payload with keys `FileHeader`, `Parties` and `Invoices`.
      */
     public function transform(Invoice $invoice, array $options = []): array
     {
@@ -41,10 +48,10 @@ public function transform(Invoice $invoice, array $options = []): array
     }
 
     /**
-     * Build file header section.
+     * Create the Facturae 3.2 file header containing schema and batch metadata.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * @param Invoice $invoice Invoice used to populate the batch identifier and total amount.
+     * @return array<string, mixed> Array with keys `SchemaVersion`, `Modality`, `InvoiceIssuerType`, and `Batch` (where `Batch` contains `BatchIdentifier`, `InvoicesCount`, and `TotalInvoicesAmount` with `TotalAmount`).
      */
     protected function buildFileHeader(Invoice $invoice): array
     {
@@ -63,10 +70,10 @@ protected function buildFileHeader(Invoice $invoice): array
     }
 
     /**
-     * Build parties section.
+     * Assembles the seller and buyer party structures for the given invoice.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * @param Invoice $invoice Invoice to extract seller and buyer information from.
+     * @return array<string, mixed> Array with 'SellerParty' and 'BuyerParty' keys containing their respective structured data.
      */
     protected function buildParties(Invoice $invoice): array
     {
@@ -77,10 +84,14 @@ protected function buildParties(Invoice $invoice): array
     }
 
     /**
-     * Build seller party data.
+     * Create the seller (supplier) party structure for the Facturae 3.2 payload.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * The structure is populated from supplier configuration and contains the
+     * TaxIdentification, PartyIdentification, AdministrativeCentres, and LegalEntity
+     * sections required by the Facturae schema.
+     *
+     * @param Invoice $invoice Invoice model (unused for most fields; provided for context).
+     * @return array<string,mixed> Seller party data matching Facturae 3.2 structure.
      */
     protected function buildSellerParty(Invoice $invoice): array
     {
@@ -119,10 +130,16 @@ protected function buildSellerParty(Invoice $invoice): array
     }
 
     /**
-     * Build buyer party data.
+     * Constructs the buyer party structure for the Facturae payload using the invoice's customer data.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * Populates tax identification, administrative centre, and legal entity sections. Address fields are
+     * provided as `AddressInSpain` for Spanish customers or `OverseasAddress` for foreign customers.
+     *
+     * @param Invoice $invoice The invoice whose customer information is used to build the buyer party.
+     * @return array<string,mixed> Array with keys:
+     *   - `TaxIdentification`: contains `PersonTypeCode`, `ResidenceTypeCode`, and `TaxIdentificationNumber`.
+     *   - `AdministrativeCentres`: contains `AdministrativeCentre` with `CentreCode`, `RoleTypeCode`, `Name` and an address block (`AddressInSpain` or `OverseasAddress`).
+     *   - `LegalEntity`: contains `CorporateName` and the same address block used in `AdministrativeCentres`.
      */
     protected function buildBuyerParty(Invoice $invoice): array
     {
@@ -172,11 +189,12 @@ protected function buildBuyerParty(Invoice $invoice): array
     }
 
     /**
-     * Build invoice data.
+     * Assembles the invoice sections required for the Facturae 3.2 invoice payload.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<string, mixed>
+     * Returns an associative array containing the invoice parts used in the payload:
+     * `InvoiceHeader`, `InvoiceIssueData`, `TaxesOutputs`, `InvoiceTotals`, `Items`, and `PaymentDetails`.
+     *
+     * @return array<string, mixed> Associative array keyed by Facturae element names with their corresponding data.
      */
     protected function buildInvoice(Invoice $invoice, string $currencyCode): array
     {
@@ -208,11 +226,18 @@ protected function buildInvoiceHeader(Invoice $invoice, string $currencyCode): a
     }
 
     /**
-     * Build invoice issue data.
-     *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
-     */
+         * Builds the invoice issuance metadata required by the Facturae payload.
+         *
+         * Returns an associative array containing the issue date, invoice and tax currency codes,
+         * and the language code used for the invoice.
+         *
+         * @param Invoice $invoice The invoice model from which dates and currency are derived.
+         * @return array<string, mixed> An array with keys:
+         *                              - `IssueDate`: the invoice issue date in Y-m-d format,
+         *                              - `InvoiceCurrencyCode`: the invoice currency code,
+         *                              - `TaxCurrencyCode`: the tax currency code,
+         *                              - `LanguageName`: the language code (e.g., 'es').
+         */
     protected function buildInvoiceIssueData(Invoice $invoice): array
     {
         return [
@@ -224,11 +249,11 @@ protected function buildInvoiceIssueData(Invoice $invoice): array
     }
 
     /**
-     * Build taxes outputs section.
+     * Assemble tax output entries grouped by tax rate for the Facturae payload.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice whose items will be grouped by tax rate to produce tax entries.
+     * @param string $currencyCode The currency code used when formatting monetary amounts.
+     * @return array<string, mixed> An array with a `Tax` key containing a list of tax group entries. Each entry includes a `Tax` structure with `TaxTypeCode`, `TaxRate`, `TaxableBase['TotalAmount']`, and `TaxAmount['TotalAmount']` formatted as strings with two decimal places.
      */
     protected function buildTaxesOutputs(Invoice $invoice, string $currencyCode): array
     {
@@ -270,11 +295,18 @@ protected function buildTaxesOutputs(Invoice $invoice, string $currencyCode): ar
     }
 
     /**
-     * Build invoice totals.
+     * Assembles invoice total amounts formatted for the Facturae payload.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice model providing subtotal and total amounts.
+     * @param string $currencyCode The invoice currency code (used for context; amounts are formatted to two decimals).
+     * @return array<string, mixed> An associative array with the following keys:
+     *                              - `TotalGrossAmount`: subtotal formatted with 2 decimals.
+     *                              - `TotalGrossAmountBeforeTaxes`: subtotal formatted with 2 decimals.
+     *                              - `TotalTaxOutputs`: tax amount (invoice total minus subtotal) formatted with 2 decimals.
+     *                              - `TotalTaxesWithheld`: taxes withheld, represented as `'0.00'`.
+     *                              - `InvoiceTotal`: invoice total formatted with 2 decimals.
+     *                              - `TotalOutstandingAmount`: outstanding amount formatted with 2 decimals.
+     *                              - `TotalExecutableAmount`: executable amount formatted with 2 decimals.
      */
     protected function buildInvoiceTotals(Invoice $invoice, string $currencyCode): array
     {
@@ -292,11 +324,11 @@ protected function buildInvoiceTotals(Invoice $invoice, string $currencyCode): a
     }
 
     /**
-     * Build invoice items.
+     * Map invoice items to Facturae 3.2 `InvoiceLine` structures.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice whose items will be converted into line entries.
+     * @param string $currencyCode Currency ISO code used for monetary formatting.
+     * @return array<string, mixed> An array with the key `InvoiceLine` containing a list of line entries formatted for Facturae (each entry includes quantities, unit price, totals and tax breakdowns).
      */
     protected function buildItems(Invoice $invoice, string $currencyCode): array
     {
@@ -332,11 +364,14 @@ protected function buildItems(Invoice $invoice, string $currencyCode): array
     }
 
     /**
-     * Build payment details.
+     * Constructs the payment details structure containing a single installment.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice used to populate the installment due date and amount.
+     * @param string $currencyCode The currency code (ISO 4217) associated with the installment amount.
+     * @return array<string,mixed> An array with an 'Installment' entry containing:
+     *                              - 'InstallmentDueDate' (string, Y-m-d),
+     *                              - 'InstallmentAmount' (string, formatted with two decimals),
+     *                              - 'PaymentMeans' (string, payment method code, e.g. '04' for transfer).
      */
     protected function buildPaymentDetails(Invoice $invoice, string $currencyCode): array
     {
@@ -350,7 +385,11 @@ protected function buildPaymentDetails(Invoice $invoice, string $currencyCode):
     }
 
     /**
-     * {@inheritdoc}
+     * Produce a Facturae 3.2 XML representation for the given invoice.
+     *
+     * @param Invoice $invoice The invoice to convert.
+     * @param array $options Optional transform options.
+     * @return string A string containing the Facturae 3.2 XML payload for the invoice. Current implementation returns a pretty-printed JSON representation of the prepared payload as a placeholder.
      */
     public function generateXml(Invoice $invoice, array $options = []): string
     {
@@ -361,8 +400,11 @@ public function generateXml(Invoice $invoice, array $options = []): string
     }
 
     /**
-     * {@inheritdoc}
-     */
+         * Validate Facturae-specific requirements for the given invoice.
+         *
+         * @param Invoice $invoice The invoice to validate.
+         * @return string[] An array of validation error messages; empty if no errors.
+         */
     protected function validateFormatSpecific(Invoice $invoice): array
     {
         $errors = [];
@@ -376,10 +418,10 @@ protected function validateFormatSpecific(Invoice $invoice): array
     }
 
     /**
-     * Extract series code from invoice number.
+     * Extracts the leading alphabetic series code from an invoice number.
      *
-     * @param string $invoiceNumber
-     * @return string
+     * @param string $invoiceNumber Invoice identifier that may start with a letter-based series.
+     * @return string The extracted series code (leading uppercase letters), or 'A' if none are present.
      */
     protected function extractSeriesCode(string $invoiceNumber): string
     {
@@ -392,14 +434,14 @@ protected function extractSeriesCode(string $invoiceNumber): string
     }
 
     /**
-     * Get tax rate from invoice item.
+     * Retrieve the tax rate for an invoice item.
      *
-     * @param mixed $item
-     * @return float
+     * @param mixed $item Invoice item expected to contain a `tax_rate` property or key.
+     * @return float The tax rate to apply; `21.0` if the item does not specify one.
      */
     protected function getTaxRate($item): float
     {
         // Default Spanish VAT rate is 21%
         return $item->tax_rate ?? 21.0;
     }
-}
+}
\ No newline at end of file
diff --git a/Modules/Invoices/Peppol/FormatHandlers/FatturaPaHandler.php b/Modules/Invoices/Peppol/FormatHandlers/FatturaPaHandler.php
index 846c3828..f2c38ab3 100644
--- a/Modules/Invoices/Peppol/FormatHandlers/FatturaPaHandler.php
+++ b/Modules/Invoices/Peppol/FormatHandlers/FatturaPaHandler.php
@@ -17,7 +17,7 @@
 class FatturaPaHandler extends BaseFormatHandler
 {
     /**
-     * Constructor.
+     * Initialize the handler configured for the FatturaPA 1.2 Peppol document format.
      */
     public function __construct()
     {
@@ -25,8 +25,16 @@ public function __construct()
     }
 
     /**
-     * {@inheritdoc}
-     */
+         * Convert an Invoice into the FatturaPA 1.2 data structure.
+         *
+         * Builds the top-level array expected for a FatturaElettronica document containing header and body sections.
+         *
+         * @param Invoice $invoice The invoice to transform.
+         * @param array $options Optional transformation flags and overrides.
+         * @return array An associative array with keys:
+         *               - `FatturaElettronicaHeader`: header data for the electronic invoice.
+         *               - `FatturaElettronicaBody`: body data for the electronic invoice.
+         */
     public function transform(Invoice $invoice, array $options = []): array
     {
         $customer = $invoice->customer;
@@ -39,10 +47,10 @@ public function transform(Invoice $invoice, array $options = []): array
     }
 
     /**
-     * Build FatturaPA header section.
+     * Build the FatturaPA electronic invoice header for the given invoice.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice used to populate header sections.
+     * @return array<string,mixed> Array with 'DatiTrasmissione', 'CedentePrestatore' and 'CessionarioCommittente' entries.
      */
     protected function buildHeader(Invoice $invoice): array
     {
@@ -54,10 +62,10 @@ protected function buildHeader(Invoice $invoice): array
     }
 
     /**
-     * Build transmission data section.
+     * Constructs the FatturaPA DatiTrasmissione (transmission data) for the given invoice.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice used to populate transmission fields.
+     * @return array<string, mixed> Array containing `IdTrasmittente` (with `IdPaese` and `IdCodice`), `ProgressivoInvio`, `FormatoTrasmissione`, and `CodiceDestinatario`.
      */
     protected function buildTransmissionData(Invoice $invoice): array
     {
@@ -73,11 +81,25 @@ protected function buildTransmissionData(Invoice $invoice): array
     }
 
     /**
-     * Build supplier data section.
-     *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
-     */
+         * Constructs the supplier (CedentePrestatore) data structure required by FatturaPA header.
+         *
+         * The returned array contains the supplier fiscal and registry information under `DatiAnagrafici`
+         * and the supplier address under `Sede`.
+         *
+         * @param Invoice $invoice Invoice instance (unused directly; kept for interface consistency).
+         * @return array<string, mixed> Array with keys:
+         *                              - `DatiAnagrafici`: [
+         *                                  `IdFiscaleIVA` => ['IdPaese' => string, 'IdCodice' => string],
+         *                                  `Anagrafica` => ['Denominazione' => string|null],
+         *                                  `RegimeFiscale` => string
+         *                                ]
+         *                              - `Sede`: [
+         *                                  `Indirizzo` => string|null,
+         *                                  `CAP` => string|null,
+         *                                  `Comune` => string|null,
+         *                                  `Nazione` => string
+         *                                ]
+         */
     protected function buildSupplierData(Invoice $invoice): array
     {
         return [
@@ -101,10 +123,14 @@ protected function buildSupplierData(Invoice $invoice): array
     }
 
     /**
-     * Build customer data section.
+     * Constructs the customer data structure used in the FatturaPA header.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * @param Invoice $invoice Invoice containing the customer information.
+     * @return array<string, mixed> Array with keys:
+     *   - `DatiAnagrafici`: contains `CodiceFiscale` (customer tax code or empty string)
+     *     and `Anagrafica` with `Denominazione` (company name or customer name).
+     *   - `Sede`: contains address fields `Indirizzo`, `CAP`, `Comune`, and `Nazione`
+     *     (country code, defaults to "IT" when absent).
      */
     protected function buildCustomerData(Invoice $invoice): array
     {
@@ -127,11 +153,14 @@ protected function buildCustomerData(Invoice $invoice): array
     }
 
     /**
-     * Build FatturaPA body section.
+     * Assembles the body section of a FatturaPA 1.2 document.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice to convert into FatturaPA body data.
+     * @param string $currencyCode ISO 4217 currency code to format monetary fields.
+     * @return array<string,mixed> Associative array with keys:
+     *                             - `DatiGenerali`: general document data,
+     *                             - `DatiBeniServizi`: line items and tax summary,
+     *                             - `DatiPagamento`: payment terms and details.
      */
     protected function buildBody(Invoice $invoice, string $currencyCode): array
     {
@@ -143,10 +172,14 @@ protected function buildBody(Invoice $invoice, string $currencyCode): array
     }
 
     /**
-     * Build general invoice data.
+     * Builds the 'DatiGeneraliDocumento' section for a FatturaPA invoice.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice to extract general document fields from.
+     * @return array<string, mixed> Array with a single key 'DatiGeneraliDocumento' containing:
+     *                              - 'TipoDocumento' (document type code),
+     *                              - 'Divisa' (currency code),
+     *                              - 'Data' (invoice date in 'Y-m-d' format),
+     *                              - 'Numero' (invoice number).
      */
     protected function buildGeneralData(Invoice $invoice): array
     {
@@ -161,11 +194,21 @@ protected function buildGeneralData(Invoice $invoice): array
     }
 
     /**
-     * Build items data section.
+     * Construct the items section with detailed line entries and the aggregated tax summary.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<string, mixed>
+     * Each line in `DettaglioLinee` contains numeric and descriptive fields for a single invoice item.
+     *
+     * @param Invoice $invoice The invoice whose items will be converted into line entries.
+     * @param string $currencyCode ISO 4217 currency code used for the line amounts.
+     * @return array<string, mixed> An array with two keys:
+     *                              - `DettaglioLinee`: array of line entries, each containing:
+     *                                  - `NumeroLinea`: line number (1-based).
+     *                                  - `Descrizione`: item description.
+     *                                  - `Quantita`: quantity formatted with two decimals.
+     *                                  - `PrezzoUnitario`: unit price formatted with two decimals.
+     *                                  - `PrezzoTotale`: total price for the line formatted with two decimals.
+     *                                  - `AliquotaIVA`: VAT rate for the line formatted with two decimals.
+     *                              - `DatiRiepilogo`: tax summary grouped by VAT rate (base and tax amounts).
      */
     protected function buildItemsData(Invoice $invoice, string $currencyCode): array
     {
@@ -187,11 +230,17 @@ protected function buildItemsData(Invoice $invoice, string $currencyCode): array
     }
 
     /**
-     * Build tax summary.
-     *
-     * @param Invoice $invoice
-     * @return array<array<string, mixed>>
-     */
+         * Builds the VAT summary grouped by VAT rate.
+         *
+         * Groups invoice items by their VAT rate and returns an array of summary entries.
+         * Each entry contains:
+         * - `AliquotaIVA`: VAT rate as a string formatted with two decimals.
+         * - `ImponibileImporto`: taxable base amount as a string formatted with two decimals.
+         * - `Imposta`: tax amount as a string formatted with two decimals.
+         *
+         * @param Invoice $invoice The invoice to summarize.
+         * @return array<int, array<string, mixed>> Array of summary entries keyed numerically.
+         */
     protected function buildTaxSummary(Invoice $invoice): array
     {
         // Group items by tax rate
@@ -225,10 +274,12 @@ protected function buildTaxSummary(Invoice $invoice): array
     }
 
     /**
-     * Build payment data section.
+     * Assemble the payment section for the FatturaPA body.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * @param Invoice $invoice Invoice used to obtain the payment due date and amount.
+     * @return array<string,mixed> Payment data with keys:
+     *                             - 'CondizioniPagamento': payment condition code,
+     *                             - 'DettaglioPagamento': array of payment entries each containing 'ModalitaPagamento', 'DataScadenzaPagamento', and 'ImportoPagamento'.
      */
     protected function buildPaymentData(Invoice $invoice): array
     {
@@ -245,8 +296,12 @@ protected function buildPaymentData(Invoice $invoice): array
     }
 
     /**
-     * {@inheritdoc}
-     */
+         * Generate the FatturaPA-compliant XML representation for the given invoice.
+         *
+         * @param Invoice $invoice The invoice to convert.
+         * @param array $options Optional transformation options.
+         * @return string The FatturaPA XML as a string; currently returns a JSON-formatted string of the transformed data as a placeholder.
+         */
     public function generateXml(Invoice $invoice, array $options = []): string
     {
         $data = $this->transform($invoice, $options);
@@ -256,8 +311,11 @@ public function generateXml(Invoice $invoice, array $options = []): string
     }
 
     /**
-     * {@inheritdoc}
-     */
+         * Validate FatturaPA-specific requirements for the given invoice.
+         *
+         * @param Invoice $invoice The invoice to validate.
+         * @return string[] List of validation error messages; empty array if there are no validation errors.
+         */
     protected function validateFormatSpecific(Invoice $invoice): array
     {
         $errors = [];
@@ -276,10 +334,10 @@ protected function validateFormatSpecific(Invoice $invoice): array
     }
 
     /**
-     * Extract ID code from VAT number (remove country prefix).
+     * Return the VAT identifier without the country prefix.
      *
-     * @param string|null $vatNumber
-     * @return string
+     * @param string|null $vatNumber VAT number possibly prefixed with a country code (e.g., "IT12345678901").
+     * @return string The VAT identifier with any leading "IT" removed; returns an empty string when the input is null or empty.
      */
     protected function extractIdCodice(?string $vatNumber): string
     {
@@ -292,14 +350,14 @@ protected function extractIdCodice(?string $vatNumber): string
     }
 
     /**
-     * Get VAT rate from invoice item.
-     *
-     * @param mixed $item
-     * @return float
-     */
+         * Obtain the VAT rate percentage for an invoice item.
+         *
+         * @param mixed $item Invoice item expected to expose a numeric `tax_rate` property (percentage).
+         * @return float The VAT percentage to apply (uses the item's `tax_rate` if present, otherwise 22.0).
+         */
     protected function getVatRate($item): float
     {
         // Assuming the item has a tax_rate or we use default Italian VAT rate
         return $item->tax_rate ?? 22.0; // 22% is standard Italian VAT
     }
-}
+}
\ No newline at end of file
diff --git a/Modules/Invoices/Peppol/FormatHandlers/OioublHandler.php b/Modules/Invoices/Peppol/FormatHandlers/OioublHandler.php
index fbe4bd79..2cb20cc6 100644
--- a/Modules/Invoices/Peppol/FormatHandlers/OioublHandler.php
+++ b/Modules/Invoices/Peppol/FormatHandlers/OioublHandler.php
@@ -17,7 +17,7 @@
 class OioublHandler extends BaseFormatHandler
 {
     /**
-     * Constructor.
+     * Initialize the handler for the OIOUBL Peppol document format.
      */
     public function __construct()
     {
@@ -25,8 +25,18 @@ public function __construct()
     }
 
     /**
-     * {@inheritdoc}
-     */
+         * Builds an OIOUBL 2.0 representation of the given invoice as an associative array.
+         *
+         * The returned array contains the core OIOUBL document fields and nested sections:
+         * ubl_version_id, customization_id, profile_id, id, issue_date, invoice_type_code,
+         * document_currency_code, accounting_cost, accounting_supplier_party,
+         * accounting_customer_party, payment_means, payment_terms, tax_total,
+         * legal_monetary_total, and invoice_line.
+         *
+         * @param Invoice $invoice The invoice to transform.
+         * @param array $options Optional transform options.
+         * @return array The invoice represented as an OIOUBL-structured associative array.
+         */
     public function transform(Invoice $invoice, array $options = []): array
     {
         $customer = $invoice->customer;
@@ -67,11 +77,11 @@ public function transform(Invoice $invoice, array $options = []): array
     }
 
     /**
-     * Build supplier party.
+     * Construct the supplier party block for the OIOUBL document using configured supplier data and the provided endpoint scheme.
      *
-     * @param Invoice $invoice
-     * @param mixed $endpointScheme
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice being transformed (unused except for context).
+     * @param mixed $endpointScheme Endpoint scheme object whose `value` property is used as the endpoint scheme identifier.
+     * @return array<string,mixed> Array representing the supplier `party` structure for the OIOUBL document.
      */
     protected function buildSupplierParty(Invoice $invoice, $endpointScheme): array
     {
@@ -121,11 +131,14 @@ protected function buildSupplierParty(Invoice $invoice, $endpointScheme): array
     }
 
     /**
-     * Build customer party.
+     * Construct the OIOUBL customer party block for the invoice.
+     *
+     * Builds a nested array representing the customer party including endpoint identification,
+     * party identification (DK:CVR), party name, postal address, legal entity, and contact details.
      *
-     * @param Invoice $invoice
-     * @param mixed $endpointScheme
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice containing customer information.
+     * @param mixed $endpointScheme An object with a `value` property used as the endpoint scheme identifier.
+     * @return array<string, mixed> Nested array representing the customer party section of the OIOUBL document.
      */
     protected function buildCustomerParty(Invoice $invoice, $endpointScheme): array
     {
@@ -168,10 +181,15 @@ protected function buildCustomerParty(Invoice $invoice, $endpointScheme): array
     }
 
     /**
-     * Build payment means.
+     * Constructs the payment means section for the given invoice.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice to build payment means for.
+     * @return array<string, mixed> An associative array with keys:
+     *                             - `payment_means_code`: string, code '31' for international bank transfer.
+     *                             - `payment_due_date`: string, due date in `YYYY-MM-DD` format.
+     *                             - `payment_id`: string, the invoice number.
+     *                             - `payee_financial_account`: array with `id` (account identifier) and
+     *                               `financial_institution_branch` containing `id` (bank SWIFT/BIC).
      */
     protected function buildPaymentMeans(Invoice $invoice): array
     {
@@ -189,11 +207,13 @@ protected function buildPaymentMeans(Invoice $invoice): array
     }
 
     /**
-     * Build payment terms.
-     *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
-     */
+         * Build payment terms for the invoice, including a human-readable note and settlement period.
+         *
+         * @param Invoice $invoice The invoice to derive payment terms from.
+         * @return array<string, mixed> An array containing:
+         *                              - `note` (string): A message like "Payment due within X days".
+         *                              - `settlement_period` (array): Contains `end_date` (string, YYYY-MM-DD) for the settlement end.
+         */
     protected function buildPaymentTerms(Invoice $invoice): array
     {
         $daysUntilDue = $invoice->invoiced_at->diffInDays($invoice->invoice_due_at);
@@ -207,12 +227,20 @@ protected function buildPaymentTerms(Invoice $invoice): array
     }
 
     /**
-     * Build tax total.
-     *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<string, mixed>
-     */
+         * Builds the invoice-level tax total and per-rate tax subtotals.
+         *
+         * Computes the total tax (invoice total minus invoice subtotal), groups invoice items by tax rate,
+         * and produces a list of tax subtotals for each rate with taxable base and tax amount.
+         *
+         * @param Invoice $invoice The invoice used to compute tax bases and amounts.
+         * @param string $currencyCode ISO currency code to attach to monetary values.
+         * @return array<string, mixed> An array containing:
+         *     - `tax_amount`: ['value' => string (formatted to 2 decimals), 'currency_id' => string]
+         *     - `tax_subtotal`: array of entries each with:
+         *         - `taxable_amount`: ['value' => string (2 decimals), 'currency_id' => string]
+         *         - `tax_amount`: ['value' => string (2 decimals), 'currency_id' => string]
+         *         - `tax_category`: ['id' => 'S'|'Z', 'percent' => float, 'tax_scheme' => ['id' => 'VAT']]
+         */
     protected function buildTaxTotal(Invoice $invoice, string $currencyCode): array
     {
         $taxAmount = $invoice->invoice_total - $invoice->invoice_subtotal;
@@ -266,11 +294,15 @@ protected function buildTaxTotal(Invoice $invoice, string $currencyCode): array
     }
 
     /**
-     * Build monetary total.
+     * Construct the monetary totals section for the given invoice.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice to derive totals from.
+     * @param string $currencyCode Currency code used for all returned amounts.
+     * @return array<string, mixed> An associative array with keys:
+     *                             - `line_extension_amount`: array with `value` (subtotal as string formatted to 2 decimals) and `currency_id`.
+     *                             - `tax_exclusive_amount`: array with `value` (subtotal) and `currency_id`.
+     *                             - `tax_inclusive_amount`: array with `value` (total amount) and `currency_id`.
+     *                             - `payable_amount`: array with `value` (total amount) and `currency_id`.
      */
     protected function buildMonetaryTotal(Invoice $invoice, string $currencyCode): array
     {
@@ -297,11 +329,16 @@ protected function buildMonetaryTotal(Invoice $invoice, string $currencyCode): a
     }
 
     /**
-     * Build invoice lines.
+     * Convert invoice items into an array of OIOUBL invoice line entries.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<int, array<string, mixed>>
+     * Each line entry contains: sequential `id`; `invoiced_quantity` with value and unit code; `line_extension_amount`
+     * and `price` values annotated with the provided currency; `accounting_cost`; and an `item` block including
+     * description, name, seller item id and a `classified_tax_category` (id 'S' for taxed lines, 'Z' for zero rate)
+     * with the tax percent and tax scheme.
+     *
+     * @param Invoice $invoice The invoice whose items will be converted into lines.
+     * @param string $currencyCode ISO currency code used for monetary values in each line.
+     * @return array<int, array<string, mixed>> Array of invoice line structures suitable for OIOUBL output.
      */
     protected function buildInvoiceLines(Invoice $invoice, string $currencyCode): array
     {
@@ -345,7 +382,14 @@ protected function buildInvoiceLines(Invoice $invoice, string $currencyCode): ar
     }
 
     /**
-     * {@inheritdoc}
+     * Generate an OIOUBL XML representation of the given invoice.
+     *
+     * Converts the invoice into the OIOUBL structure and returns it as an XML string.
+     * Currently this method returns a JSON-formatted placeholder of the transformed data.
+     *
+     * @param Invoice $invoice The invoice to convert.
+     * @param array $options Additional options forwarded to the transform step.
+     * @return string The OIOUBL XML string, or a JSON-formatted placeholder of the transformed data.
      */
     public function generateXml(Invoice $invoice, array $options = []): string
     {
@@ -356,7 +400,12 @@ public function generateXml(Invoice $invoice, array $options = []): string
     }
 
     /**
-     * {@inheritdoc}
+     * Validate OIOUBL-specific invoice requirements.
+     *
+     * Checks that a supplier CVR (VAT number) is configured and that the invoice's customer has a Peppol ID.
+     *
+     * @param Invoice $invoice The invoice to validate.
+     * @return array Array of validation error messages; empty if there are no violations.
      */
     protected function validateFormatSpecific(Invoice $invoice): array
     {
@@ -375,11 +424,11 @@ protected function validateFormatSpecific(Invoice $invoice): array
         return $errors;
     }
 
-    /**
-     * Get accounting cost code.
+    / **
+     * Uses the invoice reference as the OIOUBL accounting cost code.
      *
-     * @param Invoice $invoice
-     * @return string
+     * @param Invoice $invoice The invoice to read the reference from.
+     * @return string The invoice reference used as accounting cost, or an empty string if none.
      */
     protected function getAccountingCost(Invoice $invoice): string
     {
@@ -388,24 +437,24 @@ protected function getAccountingCost(Invoice $invoice): string
     }
 
     /**
-     * Get line accounting cost code.
-     *
-     * @param mixed $item
-     * @return string
-     */
+         * Retrieve the accounting cost code for a single invoice line.
+         *
+         * @param mixed $item Invoice line item object; expected to have an `accounting_cost` property.
+         * @return string The line's accounting cost code, or an empty string if none is set.
+         */
     protected function getLineAccountingCost($item): string
     {
         return $item->accounting_cost ?? '';
     }
 
     /**
-     * Get tax rate from invoice item.
-     *
-     * @param mixed $item
-     * @return float
-     */
+         * Return the tax rate for an invoice item, defaulting to 25.0 if the item does not specify one.
+         *
+         * @param mixed $item Invoice line item object; may provide a `tax_rate` property.
+         * @return float The tax rate as a percentage (e.g., 25.0).
+         */
     protected function getTaxRate($item): float
     {
         return $item->tax_rate ?? 25.0; // Standard Danish VAT rate
     }
-}
+}
\ No newline at end of file
diff --git a/Modules/Invoices/Peppol/FormatHandlers/ZugferdHandler.php b/Modules/Invoices/Peppol/FormatHandlers/ZugferdHandler.php
index 85cea861..5f7502ca 100644
--- a/Modules/Invoices/Peppol/FormatHandlers/ZugferdHandler.php
+++ b/Modules/Invoices/Peppol/FormatHandlers/ZugferdHandler.php
@@ -17,9 +17,11 @@
 class ZugferdHandler extends BaseFormatHandler
 {
     /**
-     * Constructor.
+     * Create a ZugferdHandler for the specified Peppol document format.
      *
-     * @param PeppolDocumentFormat|null $format Defaults to ZUGFeRD 2.0
+     * If null, the handler defaults to ZUGFERD 2.0 (Factur‑X compatible).
+     *
+     * @param PeppolDocumentFormat|null $format The target ZUGFeRD/Factur‑X format or null to use the default.
      */
     public function __construct(?PeppolDocumentFormat $format = null)
     {
@@ -27,7 +29,11 @@ public function __construct(?PeppolDocumentFormat $format = null)
     }
 
     /**
-     * {@inheritdoc}
+     * Builds a ZUGFeRD (CII) document structure for the provided invoice using the handler's configured format.
+     *
+     * @param Invoice $invoice The invoice to transform into a ZUGFeRD payload.
+     * @param array $options Optional transformation options (unused by default; implementation-specific).
+     * @return array An associative array representing the ZUGFeRD (CII) document structure conforming to either ZUGFeRD 1.0 or 2.0 depending on the handler configuration.
      */
     public function transform(Invoice $invoice, array $options = []): array
     {
@@ -86,10 +92,10 @@ protected function buildZugferd20Structure(Invoice $invoice): array
     }
 
     /**
-     * Build header exchanged document (ZUGFeRD 1.0).
+     * Create the HeaderExchangedDocument structure for ZUGFeRD 1.0 using invoice data.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * @param Invoice $invoice Invoice whose number and issue date populate the header.
+     * @return array<string, mixed> Associative array representing the HeaderExchangedDocument (ID, Name, TypeCode, IssueDateTime).
      */
     protected function buildHeaderExchangedDocument(Invoice $invoice): array
     {
@@ -107,9 +113,9 @@ protected function buildHeaderExchangedDocument(Invoice $invoice): array
     }
 
     /**
-     * Build document context (ZUGFeRD 2.0).
+     * Builds the ZUGFeRD 2.0 document context identifying the basic-compliance guideline.
      *
-     * @return array<string, mixed>
+     * @return array<string, mixed> Associative array containing `ram:GuidelineSpecifiedDocumentContextParameter` with `ram:ID` set to the ZUGFeRD 2.0 basic-profile URN.
      */
     protected function buildDocumentContext20(): array
     {
@@ -121,11 +127,14 @@ protected function buildDocumentContext20(): array
     }
 
     /**
-     * Build exchanged document (ZUGFeRD 2.0).
-     *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
-     */
+         * Constructs the ZUGFeRD 2.0 ExchangedDocument block from the invoice metadata.
+         *
+         * @param Invoice $invoice Invoice providing the document ID and issue date.
+         * @return array<string,mixed> Associative array with keys:
+         *                             - `ram:ID` (invoice number),
+         *                             - `ram:TypeCode` (invoice type code, "380"),
+         *                             - `ram:IssueDateTime` containing `udt:DateTimeString` with `@format` "102" and the issue date in `Ymd` format.
+         */
     protected function buildExchangedDocument20(Invoice $invoice): array
     {
         return [
@@ -141,11 +150,13 @@ protected function buildExchangedDocument20(Invoice $invoice): array
     }
 
     /**
-     * Build supply chain trade transaction (ZUGFeRD 1.0).
+     * Assembles the ApplicableSupplyChainTradeTransaction structure for ZUGFeRD 1.0.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<string, mixed>
+     * @param string $currencyCode ISO 4217 currency code used for monetary amount fields.
+     * @return array<string,mixed> Nested array with keys:
+     *                             - 'ApplicableSupplyChainTradeAgreement' => seller/buyer trade party blocks,
+     *                             - 'ApplicableSupplyChainTradeDelivery' => delivery event block,
+     *                             - 'ApplicableSupplyChainTradeSettlement' => settlement and monetary summation block.
      */
     protected function buildSupplyChainTradeTransaction10(Invoice $invoice, string $currencyCode): array
     {
@@ -173,10 +184,13 @@ protected function buildSupplyChainTradeTransaction20(Invoice $invoice, string $
     }
 
     /**
-     * Build trade agreement (ZUGFeRD 1.0).
+     * Builds the ZUGFeRD 1.0 trade agreement section containing seller and buyer party information.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * The returned array contains keyed blocks for `SellerTradeParty` and `BuyerTradeParty`, including
+     * postal address fields and, for the seller, a tax registration entry with VAT scheme ID.
+     *
+     * @param Invoice $invoice Invoice object used to source buyer details.
+     * @return array<string, mixed> Associative array representing the ApplicableSupplyChainTradeTransaction trade agreement portion for ZUGFeRD 1.0.
      */
     protected function buildTradeAgreement10(Invoice $invoice): array
     {
@@ -249,10 +263,10 @@ protected function buildTradeAgreement20(Invoice $invoice): array
     }
 
     /**
-     * Build trade delivery (ZUGFeRD 1.0).
+     * Builds the ZUGFeRD 1.0 ActualDeliverySupplyChainEvent using the invoice's issue date.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * @param Invoice $invoice The invoice whose invoiced_at date is used for the occurrence date.
+     * @return array<string, mixed> Array representing the ActualDeliverySupplyChainEvent with a `DateTimeString` in format `102` (YYYYMMDD).
      */
     protected function buildTradeDelivery10(Invoice $invoice): array
     {
@@ -269,10 +283,10 @@ protected function buildTradeDelivery10(Invoice $invoice): array
     }
 
     /**
-     * Build trade delivery (ZUGFeRD 2.0).
+     * Builds the trade delivery block for ZUGFeRD 2.0 with the delivery occurrence date.
      *
-     * @param Invoice $invoice
-     * @return array<string, mixed>
+     * @param Invoice $invoice Invoice whose `invoiced_at` date is used as the occurrence date.
+     * @return array<string,mixed> Associative array representing `ram:ActualDeliverySupplyChainEvent` with `ram:OccurrenceDateTime` containing `udt:DateTimeString` (format `102`) set to the invoice's `invoiced_at` in `Ymd` format.
      */
     protected function buildTradeDelivery20(Invoice $invoice): array
     {
@@ -289,11 +303,15 @@ protected function buildTradeDelivery20(Invoice $invoice): array
     }
 
     /**
-     * Build trade settlement (ZUGFeRD 1.0).
+     * Constructs the trade settlement section for a ZUGFeRD 1.0 invoice.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<string, mixed>
+     * The resulting array contains invoice currency, payment means (SEPA), applicable tax totals,
+     * payment terms with due date, and the monetary summation (line total, tax basis, tax total,
+     * grand total, and due payable amounts).
+     *
+     * @param Invoice $invoice The invoice to derive settlement values from.
+     * @param string $currencyCode ISO 4217 currency code used for monetary amounts.
+     * @return array<string, mixed> Array representing the SpecifiedTradeSettlement structure for ZUGFeRD 1.0.
      */
     protected function buildTradeSettlement10(Invoice $invoice, string $currencyCode): array
     {
@@ -339,11 +357,18 @@ protected function buildTradeSettlement10(Invoice $invoice, string $currencyCode
     }
 
     /**
-     * Build trade settlement (ZUGFeRD 2.0).
+     * Build the ZUGFeRD 2.0 trade settlement section for the given invoice.
      *
-     * @param Invoice $invoice
-     * @param string $currencyCode
-     * @return array<string, mixed>
+     * Returns an associative array containing the settlement information:
+     * - `ram:InvoiceCurrencyCode`
+     * - `ram:SpecifiedTradeSettlementPaymentMeans` (TypeCode "58" for SEPA)
+     * - `ram:ApplicableTradeTax` (per-rate tax totals)
+     * - `ram:SpecifiedTradePaymentTerms` (due date as `udt:DateTimeString` format 102)
+     * - `ram:SpecifiedTradeSettlementHeaderMonetarySummation` (line, tax, grand and due payable amounts)
+     *
+     * @param Invoice $invoice Invoice model providing amounts and dates.
+     * @param string $currencyCode ISO 4217 currency code used for monetary elements.
+     * @return array<string, mixed> Associative array representing the ZUGFeRD 2.0 settlement structure.
      */
     protected function buildTradeSettlement20(Invoice $invoice, string $currencyCode): array
     {
@@ -376,11 +401,18 @@ protected function buildTradeSettlement20(Invoice $invoice, string $currencyCode
         ];
     }
 
-    /**
-     * Build tax totals (ZUGFeRD 1.0).
+    /****
+     * Builds tax total entries for ZUGFeRD 1.0 grouped by tax rate.
      *
-     * @param Invoice $invoice
-     * @return array<array<string, mixed>>
+     * Each entry contains:
+     * - `CalculatedAmount`: array with `@currencyID` and numeric string value (`#`).
+     * - `TypeCode`: tax type (always `'VAT'`).
+     * - `BasisAmount`: array with `@currencyID` and numeric string value (`#`).
+     * - `CategoryCode`: `'S'` for taxable rates greater than zero, `'Z'` for zero rate.
+     * - `ApplicablePercent`: tax rate as a numeric string.
+     *
+     * @param Invoice $invoice Invoice used to compute tax groups.
+     * @return array<int,array{CalculatedAmount:array{'@currencyID':string,'#':string},TypeCode:string,BasisAmount:array{'@currencyID':string,'#':string},CategoryCode:string,ApplicablePercent:string}> Array of tax total entries suitable for ZUGFeRD 1.0.
      */
     protected function buildTaxTotals10(Invoice $invoice): array
     {
@@ -407,11 +439,15 @@ protected function buildTaxTotals10(Invoice $invoice): array
     }
 
     /**
-     * Build tax totals (ZUGFeRD 2.0).
-     *
-     * @param Invoice $invoice
-     * @return array<array<string, mixed>>
-     */
+         * Build the ZUGFeRD 2.0 tax total entries grouped by tax rate.
+         *
+         * Produces an array of RAM tax nodes where each entry contains formatted strings for
+         * `ram:CalculatedAmount`, `ram:BasisAmount`, and `ram:RateApplicablePercent`, plus
+         * `ram:TypeCode` and `ram:CategoryCode` (\"S\" for taxable rates > 0, \"Z\" for zero rate).
+         *
+         * @param Invoice $invoice Invoice to derive tax groups from.
+         * @return array<array<string, mixed>> List of tax entries suitable for inclusion in a ZUGFeRD 2.0 payload.
+         */
     protected function buildTaxTotals20(Invoice $invoice): array
     {
         $taxGroups = $this->groupTaxesByRate($invoice);
@@ -431,10 +467,14 @@ protected function buildTaxTotals20(Invoice $invoice): array
     }
 
     /**
-     * Group taxes by rate.
+     * Groups invoice tax bases and tax amounts by tax rate.
      *
-     * @param Invoice $invoice
-     * @return array<float, array<string, float>>
+     * Builds an associative array keyed by tax rate (percentage) where each value contains
+     * the cumulative 'base' (taxable amount) and 'amount' (calculated tax) for that rate,
+     * using the invoice currency values.
+     *
+     * @param Invoice $invoice The invoice whose items will be grouped.
+     * @return array<float, array<string, float>> Associative array keyed by tax rate with keys 'base' and 'amount' holding totals as floats.
      */
     protected function groupTaxesByRate(Invoice $invoice): array
     {
@@ -458,7 +498,13 @@ protected function groupTaxesByRate(Invoice $invoice): array
     }
 
     /**
-     * {@inheritdoc}
+     * Generate a string representation of the invoice's ZUGFeRD data.
+     *
+     * Converts the given invoice into the format-specific ZUGFeRD structure and returns it as a string.
+     *
+     * @param Invoice $invoice The invoice to convert into ZUGFeRD format.
+     * @param array $options Optional format-specific options.
+     * @return string The pretty-printed JSON representation of the transformed ZUGFeRD data (placeholder for the actual XML embedding).
      */
     public function generateXml(Invoice $invoice, array $options = []): string
     {
@@ -469,7 +515,10 @@ public function generateXml(Invoice $invoice, array $options = []): string
     }
 
     /**
-     * {@inheritdoc}
+     * Perform ZUGFeRD-specific validation on an invoice.
+     *
+     * @param Invoice $invoice The invoice to validate.
+     * @return string[] Array of validation error messages; empty if the invoice passes ZUGFeRD-specific checks.
      */
     protected function validateFormatSpecific(Invoice $invoice): array
     {
@@ -484,13 +533,13 @@ protected function validateFormatSpecific(Invoice $invoice): array
     }
 
     /**
-     * Get tax rate from invoice item.
-     *
-     * @param mixed $item
-     * @return float
-     */
+         * Retrieve the tax rate percent from an invoice item.
+         *
+         * @param mixed $item Invoice line item object or array expected to contain a `tax_rate` value.
+         * @return float The tax rate as a percentage (e.g., 19.0). Returns 19.0 if the item has no `tax_rate`.
+         */
     protected function getTaxRate($item): float
     {
         return $item->tax_rate ?? 19.0; // Default German VAT rate
     }
-}
+}
\ No newline at end of file