diff --git a/public/userarea/mapping_template_xls_scheme2.php b/public/userarea/mapping_template_xls_scheme2.php
index 544aed2..dd845a9 100644
--- a/public/userarea/mapping_template_xls_scheme2.php
+++ b/public/userarea/mapping_template_xls_scheme2.php
@@ -1569,9 +1569,14 @@ $apiSampleJson = $template['api_sample_json'] ?? '';
                     const mappingId = checkbox.dataset.mappingId;
                     const value = checkbox.checked ? 1 : 0;
 
-                    const checkedMainFields = document.querySelectorAll('.main-field-checkbox:checked');
+                    // Count only the other Main fields already checked in this table
+                    const otherCheckedMainFields = Array.from(
+                        document.querySelectorAll('#schemaFieldsBody .main-field-checkbox')
+                    ).filter(cb => cb !== checkbox && cb.checked);
 
-                    if (checkedMainFields.length > 2) {
+                    // If I am checking this one, I can have max 2 total:
+                    // this checkbox + max 1 other already checked
+                    if (checkbox.checked && otherCheckedMainFields.length >= 2) {
                         checkbox.checked = false;
                         alert('Puoi selezionare al massimo 2 campi Main.');
                         return;
@@ -1593,7 +1598,7 @@ $apiSampleJson = $template['api_sample_json'] ?? '';
                             if (!data.success) {
                                 console.error("❌ Error updating main_field:", data.message);
 
-                                document.querySelectorAll('.main-field-checkbox').forEach(cb => {
+                                document.querySelectorAll('#schemaFieldsBody .main-field-checkbox').forEach(cb => {
                                     cb.checked = cb.dataset.originalChecked === 'true';
                                 });
 
@@ -1601,14 +1606,14 @@ $apiSampleJson = $template['api_sample_json'] ?? '';
                                 return;
                             }
 
-                            document.querySelectorAll('.main-field-checkbox').forEach(cb => {
+                            document.querySelectorAll('#schemaFieldsBody .main-field-checkbox').forEach(cb => {
                                 cb.dataset.originalChecked = cb.checked ? 'true' : 'false';
                             });
                         })
                         .catch(error => {
                             console.error("❌ Fetch error:", error);
 
-                            document.querySelectorAll('.main-field-checkbox').forEach(cb => {
+                            document.querySelectorAll('#schemaFieldsBody .main-field-checkbox').forEach(cb => {
                                 cb.checked = cb.dataset.originalChecked === 'true';
                             });
 
@@ -1661,9 +1666,9 @@ $apiSampleJson = $template['api_sample_json'] ?? '';
             });
 
 
-            // Salva lo stato originale dei checkbox al caricamento
-            document.querySelectorAll('.main-field-checkbox').forEach(cb => {
-                cb.dataset.originalChecked = cb.checked;
+            // Save original Main checkbox state
+            document.querySelectorAll('#schemaFieldsBody .main-field-checkbox').forEach(cb => {
+                cb.dataset.originalChecked = cb.checked ? 'true' : 'false';
             });
 
             // AUTO VALUE select change -> save auto_value
diff --git a/public/userarea/update_main_field.php b/public/userarea/update_main_field.php
index 127d6d2..302c665 100644
--- a/public/userarea/update_main_field.php
+++ b/public/userarea/update_main_field.php
@@ -7,13 +7,15 @@ include('include/headscript.php');
 
 header('Content-Type: application/json');
 
-// Read JSON payload
 $data = json_decode(file_get_contents('php://input'), true);
 
 $template_id = intval($data['template_id'] ?? 0);
 $mapping_id  = intval($data['mapping_id'] ?? 0);
 $value       = intval($data['value'] ?? 0);
 
+// IMPORTANT: main_field may be ENUM('0','1'), so use string values
+$mainValue = ($value === 1) ? '1' : '0';
+
 if ($template_id <= 0 || $mapping_id <= 0) {
     echo json_encode(['success' => false, 'message' => 'Invalid IDs']);
     exit;
@@ -25,13 +27,12 @@ $pdo = $db->getConnection();
 try {
     $pdo->beginTransaction();
 
-    // If user is trying to activate a Main field, check current number of active Main fields
-    if ($value === 1) {
+    if ($mainValue === '1') {
         $stmt = $pdo->prepare("
-            SELECT COUNT(*) 
-            FROM template_mapping 
-            WHERE template_id = ? 
-              AND main_field = 1 
+            SELECT COUNT(*)
+            FROM template_mapping
+            WHERE template_id = ?
+              AND main_field = '1'
               AND id <> ?
         ");
         $stmt->execute([$template_id, $mapping_id]);
@@ -39,22 +40,23 @@ try {
 
         if ($currentMainCount >= 2) {
             $pdo->rollBack();
+
             echo json_encode([
                 'success' => false,
-                'message' => 'Maximum 2 Main fields allowed'
+                'message' => 'Maximum 2 Main fields allowed',
+                'currentMainCount' => $currentMainCount
             ]);
             exit;
         }
     }
 
-    // Update only this mapping
     $stmt = $pdo->prepare("
-        UPDATE template_mapping 
-        SET main_field = ? 
-        WHERE id = ? 
+        UPDATE template_mapping
+        SET main_field = ?
+        WHERE id = ?
           AND template_id = ?
     ");
-    $stmt->execute([$value, $mapping_id, $template_id]);
+    $stmt->execute([$mainValue, $mapping_id, $template_id]);
 
     $pdo->commit();