fix: update payment amount after discount applied

Author: rahulchaudhary2002

app/Http/Controllers/PosController.php

@@ -205,6 +205,8 @@ public function applyDiscount(Request $request, Order $order): JsonResponse
             'discount_type'   => $updated->discount_type,
             'discount_value'  => $updated->discount_value,
             'discount_amount' => $updated->discount_amount,
+            'grand_total'     => $updated->grand_total,
+            'due_amount'      => $updated->due_amount,
         ]);
     }