diff --git a/src/engine/common.md b/src/engine/common.md
index ada881082..735f8d9e0 100644
--- a/src/engine/common.md
+++ b/src/engine/common.md
@@ -98,6 +98,7 @@ The list of error codes introduced by this specification can be found below.
 | -38002 | Invalid forkchoice state | Forkchoice state is invalid / inconsistent. |
 | -38003 | Invalid payload attributes | Payload attributes are invalid / inconsistent. |
 | -38004 | Too large request | Number of requested entities is too large. |
+| -38005 | Unsupported fork | Payload belongs to a fork that is not supported. |
 
 Each error returns a `null` `data` value, except `-32000` which returns the `data` object with a `err` member that explains the error encountered.
 
diff --git a/src/engine/experimental/blob-extension.md b/src/engine/experimental/blob-extension.md
index b4cbbc6c3..501de47ae 100644
--- a/src/engine/experimental/blob-extension.md
+++ b/src/engine/experimental/blob-extension.md
@@ -63,13 +63,11 @@ The fields are encoded as follows:
 
 * method: `engine_newPayloadV3`
 * params:
-  1. [`ExecutionPayloadV1`](../paris.md#ExecutionPayloadV1) | [`ExecutionPayloadV2`](../shanghai.md#ExecutionPayloadV2) | [`ExecutionPayloadV3`](#ExecutionPayloadV3), where:
-      - `ExecutionPayloadV1` **MUST** be used if the `timestamp` value is lower than the Shanghai timestamp,
-      - `ExecutionPayloadV2` **MUST** be used if the `timestamp` value is greater or equal to the Shanghai and lower than the EIP-4844 activation timestamp,
-      - `ExecutionPayloadV3` **MUST** be used if the `timestamp` value is greater or equal to the EIP-4844 activation timestamp,
-      - Client software **MUST** return `-32602: Invalid params` error if the wrong version of the structure is used in the method call.
+  1. [`ExecutionPayloadV3`](#ExecutionPayloadV3).
   2. `Array of DATA`, 32 Bytes - Array of blob versioned hashes to validate.
 
+Client software **MUST** return `-32602: Invalid params` error unless all parameters and their fields are provided with non-`null` values.
+
 #### Response
 
 Refer to the response for `engine_newPayloadV2`.
@@ -84,6 +82,8 @@ This method follows the same specification as `engine_newPayloadV2` with the add
 
     This validation **MUST** be instantly run in all cases even during active sync process.
 
+2. Client software **MUST** return `-38005: Unsupported fork` error if the `timestamp` of the payload is less than the EIP-4844 activation timestamp.
+
 ### engine_getPayloadV3
 
 The response of this method is extended with [`BlobsBundleV1`](#blobsbundlev1) containing the blobs, their respective KZG commitments
@@ -99,10 +99,7 @@ and proofs corresponding to the `versioned_hashes` included in the blob transact
 #### Response
 
 * result: `object`
-  - `executionPayload`: [`ExecutionPayloadV1`](../paris.md#ExecutionPayloadV1) | [`ExecutionPayloadV2`](../shanghai.md#ExecutionPayloadV2) |  [`ExecutionPayloadV3`](#ExecutionPayloadV3) where:
-    - `ExecutionPayloadV1` **MUST** be returned if the payload `timestamp` is lower than the Shanghai timestamp
-    - `ExecutionPayloadV2` **MUST** be returned if the payload `timestamp` is greater or equal to the Shanghai timestamp and lower than the EIP-4844 activation timestamp
-    - `ExecutionPayloadV3` **MUST** be returned if the payload `timestamp` is greater or equal to the EIP-4844 activation timestamp
+  - `executionPayload`: [`ExecutionPayloadV3`](#ExecutionPayloadV3)
   - `blockValue` : `QUANTITY`, 256 Bits - The expected value to be received by the `feeRecipient` in wei
   - `blobsBundle`: [`BlobsBundleV1`](#BlobsBundleV1) - Bundle with data corresponding to blob transactions included into `executionPayload`
 * error: code and message set in case an exception happens while getting the payload.
@@ -117,3 +114,5 @@ Refer to the specification for `engine_getPayloadV2` with addition of the follow
    i.e. `assert verify_kzg_commitments_against_transactions(payload.transactions, bundle.commitments)` (see EIP-4844 consensus-specs).
 
 3. The call **MUST** return `blobs` and `proofs` that match the `commitments` list, i.e. `assert len(commitments) == len(blobs) == len(proofs)` and `assert verify_blob_kzg_proof_batch(bundle.blobs, bundle.commitments, bundle.proofs)`.
+
+4. Client software **MUST** return `-38005: Unsupported fork` error if the `timestamp` of the built payload is less than the EIP-4844 activation timestamp.