diff --git a/app/Http/Controllers/SapFileController.php b/app/Http/Controllers/SapFileController.php
index c120c94..3454292 100644
--- a/app/Http/Controllers/SapFileController.php
+++ b/app/Http/Controllers/SapFileController.php
@@ -218,6 +218,7 @@ class SapFileController extends Controller
 
         $serialNumbers = [];
         $remainingRow = null;
+        $invalidSerials = [];
 
         foreach ($lines as $line) {
             $values = str_getcsv($line);
@@ -231,16 +232,30 @@ class SapFileController extends Controller
             }
 
             // Collect serial number
-            $serialNumbers[] = $values[5] ?? null;
+           // $serialNumbers[] = $values[5] ?? null;
+             $serial = $values[5] ?? null;
+             $serialNumbers[] = $serial;
+
+             if ($serial == null || strlen($serial) < 13) {
+                $invalidSerials[] = $serialNumbers;
+            }
 
             // Store remaining row only once
-            if ($remainingRow === null) {
+            if ($remainingRow == null) {
                 $remainingRow = $values;
                 unset($remainingRow[5]); // remove serial number
                 $remainingRow = array_values($remainingRow); // reindex
             }
         }
 
+        if (!empty($invalidSerials)) {
+            return response()->json([
+                'status' => 'ERROR',
+                'status_description' => 'Some serial numbers are invalid (less than 13 characters)',
+                'invalid_serials' => $invalidSerials
+            ], 400);
+        }
+
         return response()->json([
             'status' => 'SUCCESS',
             'serial_numbers' => $serialNumbers,