diff --git a/API/data/TableCreation.js b/API/data/TableCreation.js
index 7508f85..e8faa94 100644
--- a/API/data/TableCreation.js
+++ b/API/data/TableCreation.js
@@ -43,7 +43,7 @@ async function createUserTable(query) {
     id INT AUTO_INCREMENT PRIMARY KEY,
     first_name VARCHAR(255) NOT NULL,
     last_name VARCHAR(255) NOT NULL,
-    identifier VARCHAR(255) NOT NULL,
+    identifier VARCHAR(255) NOT NULL UNIQUE,
     archived_date Datetime default NULL
   )`;
 
diff --git a/API/model/Managers/UserManager.js b/API/model/Managers/UserManager.js
index 31b5c84..79e10e7 100644
--- a/API/model/Managers/UserManager.js
+++ b/API/model/Managers/UserManager.js
@@ -30,7 +30,11 @@ async function add(user) {
     assert(user.email, '[UserManager.add] The email is required');
     assert(/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(user.email), '[UserManager.add] The email is not valid');
 
-    return await UserQueries.add(user);
+    try {
+        return await UserQueries.add(user);
+    } catch (e) {
+        return e;
+    }
 
 }
 
@@ -175,12 +179,11 @@ async function unarchive(id) {
  */
 async function generateSigningToken(data, documentId) {
 
-    let userId;
+    const user = await UserQueries.getByEmail(data.email);
 
-    // check for the user / add it if needed
-    if (!await UserQueries.getByEmail(data.email)) {
-        userId = await UserQueries.add(data);
-    }
+    assert(user, '[UserManager.generateSigningToken] The user is required'); // may check the addUser from the front
+
+    const userId = user.id;
 
     assert(data.email, '[UserManager.generateSigningToken] The email is required');
     assert(documentId, '[UserManager.generateSigningToken] The documentId is required');
@@ -193,10 +196,6 @@ async function generateSigningToken(data, documentId) {
         token = utils.generateRandomToken(5, false);
     }
 
-    // Get the user and version IDs
-    if (!userId) {
-        userId = (await UserQueries.getByEmail(data.email)).id;
-    }
     const versionId = (await VersionQueries.getLatest(documentId)).id;
 
     // Add the token to the database
diff --git a/FRONT/js/model/popups/SigningLinkPopup.js b/FRONT/js/model/popups/SigningLinkPopup.js
index c988ef8..293ca32 100644
--- a/FRONT/js/model/popups/SigningLinkPopup.js
+++ b/FRONT/js/model/popups/SigningLinkPopup.js
@@ -151,7 +151,10 @@ class SigningLinkPopup extends Popup {
 
         // actions to be taken when the popup is clicked
         const actions = {
-            'signing-link-copy': async (_, link) => await Utils.copyToClipboard(link),
+            'signing-link-copy': async (_, link) => {
+                await Utils.copyToClipboard(link)
+                alert('Lien copié dans le presse-papier');
+            },
             'signing-link-mailto': async (user, link) => {
                 // send the mail
                 window.location.href = `mailto:${user.identifier}?subject=Signature du document ${docName}&body=Bonjour ${user.first_name} ${user.last_name},%0D%0AMerci de signer ce document à l'adresse suivante : ${link}.%0D%0ACordialement.`;