completed group batch feature

lib/screens/gateway/gateway_screen.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_dotenv/flutter_dotenv.dart';
 import 'package:go_router/go_router.dart';
 import 'package:qpay/screens/gateway/gateway_controller.dart';
+import 'package:qpay/widgets/app_snack_bar.dart';
 import 'package:webview_flutter/webview_flutter.dart';
 
 class GatewayScreen extends StatefulWidget {
@@ -69,15 +70,11 @@ class _GatewayScreenState extends State<GatewayScreen> {
         return;
       }
 
-      ScaffoldMessenger.of(context).showSnackBar(
-        SnackBar(
-          content: Text(
-            "Payment was successful, please wait while we process your order.",
-          ),
-          behavior: SnackBarBehavior.floating,
-          backgroundColor: Colors.black87,
-          duration: const Duration(seconds: 10),
-        ),
+      AppSnackBar.show(
+        context,
+        'Payment was successful, please wait while we process your order.',
+        backgroundColor: Colors.black87,
+        duration: const Duration(seconds: 10),
       );
 
       setState(() {