diff --git a/README.md b/README.md
index 9f612e5..ce0e8ab 100644
--- a/README.md
+++ b/README.md
@@ -1,52 +1,50 @@
 # qpay-peak-flutter
 
-## Switch from Test to Live Environment
+## Environment Switching (Test vs Live)
 
-This project currently reads runtime API settings from `assets/.env` and loads Mastercard Checkout for web from `web/index.html`.
+Environment selection is command-driven with `--dart-define=APP_ENV=...`.
 
-Use the checklist below before building for production.
+- `APP_ENV=test` loads `assets/.env.test`
+- `APP_ENV=live` loads `assets/.env.live`
+- If `APP_ENV` is not provided, default is `test`
 
-### 1) Update API and simulation flags (`assets/.env`)
+For web, Mastercard Checkout is loaded dynamically from `GATEWAY_SCRIPT_URL` in the active env file, so `web/index.html` no longer needs manual test/live script edits.
 
-In `assets/.env`, make sure the active (uncommented) values are set for live:
+### Env files
 
-```dotenv
-BASE_URL=https://peakapi.qantra.co.zw/api
-SIMULATE_PAYMENT_SUCCESS=false
+Set environment-specific values in:
+
+- `assets/.env.test`
+- `assets/.env.live`
+
+Supported keys:
+
+- `BASE_URL`
+- `CLIENTID`
+- `SIMULATE_PAYMENT_SUCCESS`
+- `GATEWAY_SCRIPT_URL`
+
+### Run in Test
+
+```bash
+flutter run --dart-define=APP_ENV=test
 ```
 
-Notes:
-- Keep only one active `BASE_URL` line.
-- `SIMULATE_PAYMENT_SUCCESS` must be `false` in live to avoid fake-success payment flows.
+### Run in Live
 
-### 2) Update Mastercard Checkout script (`web/index.html`)
-
-In `web/index.html`, switch the checkout script from test to live:
-
-```html
-<script src="https://na.gateway.mastercard.com/static/checkout/checkout.min.js"></script>
+```bash
+flutter run --dart-define=APP_ENV=live
 ```
 
-And ensure the test script is not active:
+### Build in Live
 
-```html
-<!-- <script src="https://test-gateway.mastercard.com/static/checkout/checkout.min.js"></script> -->
+```bash
+flutter build web --dart-define=APP_ENV=live
+flutter build apk --dart-define=APP_ENV=live
 ```
 
-### 3) Quick pre-release verification
+### Quick pre-release checks
 
-Before release, confirm:
-- `assets/.env` points to the live API URL.
-- `assets/.env` has `SIMULATE_PAYMENT_SUCCESS=false`.
-- `web/index.html` loads `na.gateway.mastercard.com` (not `test-gateway.mastercard.com`).
-
-## Switch back to Test
-
-To return to test:
-- Restore the test `BASE_URL` in `assets/.env`.
-- Set `SIMULATE_PAYMENT_SUCCESS=true` (only if needed for local testing).
-- Re-enable the test checkout script in `web/index.html`.
-
-## Source of Truth
-
-If environment settings change in future, update this README section together with `assets/.env` and `web/index.html` so release steps stay accurate.
+- Confirm `assets/.env.live` points to the live API (`BASE_URL`).
+- Confirm `assets/.env.live` has `SIMULATE_PAYMENT_SUCCESS=false`.
+- Confirm `assets/.env.live` uses live gateway script URL in `GATEWAY_SCRIPT_URL`.
diff --git a/assets/.env.live b/assets/.env.live
new file mode 100644
index 0000000..61bcc39
--- /dev/null
+++ b/assets/.env.live
@@ -0,0 +1,5 @@
+BASE_URL=https://peakapi.qantra.co.zw/api
+CLIENTID=77433712483-ng7pntvcpf6tnjccriuqm8dbna8vvp3b.apps.googleusercontent.com
+SIMULATE_PAYMENT_SUCCESS=false
+GATEWAY_SCRIPT_URL=https://na.gateway.mastercard.com/static/checkout/checkout.min.js
+
diff --git a/assets/.env.test b/assets/.env.test
new file mode 100644
index 0000000..2d5fdc1
--- /dev/null
+++ b/assets/.env.test
@@ -0,0 +1,5 @@
+BASE_URL=http://192.168.100.85:6950/api
+CLIENTID=77433712483-ng7pntvcpf6tnjccriuqm8dbna8vvp3b.apps.googleusercontent.com
+SIMULATE_PAYMENT_SUCCESS=true
+GATEWAY_SCRIPT_URL=https://test-gateway.mastercard.com/static/checkout/checkout.min.js
+
diff --git a/lib/interop.dart b/lib/interop.dart
index 7dd7770..a671e85 100644
--- a/lib/interop.dart
+++ b/lib/interop.dart
@@ -1,7 +1,48 @@
+import 'dart:async';
 import 'dart:js_interop';
 
+import 'package:flutter_dotenv/flutter_dotenv.dart';
+import 'package:web/web.dart' as web;
+
+const String _defaultGatewayScriptUrl =
+    'https://test-gateway.mastercard.com/static/checkout/checkout.min.js';
+
+@JS('Checkout')
+external JSAny? _checkout;
+
 @JS('configure')
 external void configure(String sessionID);
 
 @JS('showEmbeddedPage')
 external void showEmbeddedPage();
+
+Future<void> ensureCheckoutScriptLoaded() async {
+  final existing = web.document.querySelector('#mastercard-checkout-script');
+  if (existing is web.HTMLScriptElement) {
+    await _waitForCheckout();
+    return;
+  }
+
+  final scriptUrl =
+      dotenv.env['GATEWAY_SCRIPT_URL'] ?? _defaultGatewayScriptUrl;
+
+  final scriptElement = web.HTMLScriptElement()
+    ..id = 'mastercard-checkout-script'
+    ..src = scriptUrl
+    ..async = true;
+
+  web.document.head?.append(scriptElement);
+  await _waitForCheckout();
+}
+
+Future<void> _waitForCheckout() async {
+  const maxAttempts = 100;
+  for (var attempt = 0; attempt < maxAttempts; attempt++) {
+    if (_checkout != null) {
+      return;
+    }
+    await Future.delayed(const Duration(milliseconds: 100));
+  }
+
+  throw StateError('Mastercard Checkout script failed to load before timeout.');
+}
diff --git a/lib/main.dart b/lib/main.dart
index f70745b..2688981 100644
--- a/lib/main.dart
+++ b/lib/main.dart
@@ -29,21 +29,34 @@ import 'package:flutter_dotenv/flutter_dotenv.dart';
 import 'package:firebase_core/firebase_core.dart';
 import 'firebase_options.dart';
 
-const String testEnv = "assets/.env";
-const String liveEnv = "assets/.env";
+const String testEnv = 'assets/.env.test';
+const String liveEnv = 'assets/.env.live';
+const String appEnv = String.fromEnvironment('APP_ENV', defaultValue: 'test');
+
+String resolveEnvFile(String env) {
+  switch (env.toLowerCase()) {
+    case 'live':
+      return liveEnv;
+    case 'test':
+    default:
+      return testEnv;
+  }
+}
 
 void main() async {
   WidgetsFlutterBinding.ensureInitialized();
-  await Firebase.initializeApp(
-    options: DefaultFirebaseOptions.currentPlatform,
-  );
+  await Firebase.initializeApp(options: DefaultFirebaseOptions.currentPlatform);
 
-  await dotenv.load(fileName: testEnv);
+  await dotenv.load(fileName: resolveEnvFile(appEnv));
   runApp(
     MultiProvider(
       providers: [
-        ChangeNotifierProvider<TransactionController>(create: (_) => TransactionController()),
-        ChangeNotifierProvider<OnboardingController>(create: (_) => OnboardingController()),
+        ChangeNotifierProvider<TransactionController>(
+          create: (_) => TransactionController(),
+        ),
+        ChangeNotifierProvider<OnboardingController>(
+          create: (_) => OnboardingController(),
+        ),
       ],
       child: const MyApp(),
     ),
diff --git a/lib/screens/gateway/gateway_web_screen.dart b/lib/screens/gateway/gateway_web_screen.dart
index 8457be9..4a1c668 100644
--- a/lib/screens/gateway/gateway_web_screen.dart
+++ b/lib/screens/gateway/gateway_web_screen.dart
@@ -60,6 +60,8 @@ class _GatewayWebScreenState extends State<GatewayWebScreen> {
   }
 
   void initIframeView() async {
+    await ensureCheckoutScriptLoaded();
+
     final uri = Uri.parse(url);
     // 2. The pathSegments property returns a list of the parts of the path.
     // For "checkout/pay/SESSION...", the segments are ["checkout", "pay", "SESSION..."].
@@ -187,10 +189,8 @@ class _GatewayWebScreenState extends State<GatewayWebScreen> {
                               horizontal: 20,
                             ),
                             child: Row(
-                              crossAxisAlignment:
-                                  CrossAxisAlignment.center,
-                              mainAxisAlignment:
-                                  MainAxisAlignment.spaceBetween,
+                              crossAxisAlignment: CrossAxisAlignment.center,
+                              mainAxisAlignment: MainAxisAlignment.spaceBetween,
                               children: [
                                 Text(
                                   'Once done on this page, check transaction status',
@@ -211,9 +211,7 @@ class _GatewayWebScreenState extends State<GatewayWebScreen> {
                                           .colorScheme
                                           .primary
                                           .withValues(alpha: 0.15),
-                                      borderRadius: BorderRadius.circular(
-                                        12,
-                                      ),
+                                      borderRadius: BorderRadius.circular(12),
                                     ),
                                     child: Text(
                                       'Check status',
@@ -224,7 +222,7 @@ class _GatewayWebScreenState extends State<GatewayWebScreen> {
                               ],
                             ),
                           ),
-                          SizedBox(height: 10,),
+                          SizedBox(height: 10),
                           SizedBox(
                             width: double.infinity,
                             height: constraints.maxHeight + 300,
diff --git a/web/index.html b/web/index.html
index 9ce5a39..8d1fbc8 100644
--- a/web/index.html
+++ b/web/index.html
@@ -33,11 +33,12 @@
 
   <title>Velocity</title>
   <link rel="manifest" href="manifest.json">
-  <script src="https://na.gateway.mastercard.com/static/checkout/checkout.min.js">
-  </script>
-  <!-- <script src="https://test-gateway.mastercard.com/static/checkout/checkout.min.js"></script> -->
   <script type="text/javascript">
     function configure(sessionID) {
+      if (typeof Checkout === 'undefined') {
+        throw new Error('Checkout SDK not loaded.');
+      }
+
       Checkout.configure({
         session: {
             id:  sessionID
@@ -46,6 +47,10 @@
     }
 
     function showEmbeddedPage() {
+      if (typeof Checkout === 'undefined') {
+        throw new Error('Checkout SDK not loaded.');
+      }
+
       Checkout.showEmbeddedPage('#embed-target');
     }
   </script>