diff --git a/lib/Iamport_certification.dart b/lib/iamport_certification.dart
similarity index 72%
rename from lib/Iamport_certification.dart
rename to lib/iamport_certification.dart
index 44894bf..031cb83 100644
--- a/lib/Iamport_certification.dart
+++ b/lib/iamport_certification.dart
@@ -13,16 +13,9 @@ import 'package:iamport_flutter/widget/iamport_webview.dart';
 import 'package:iamport_webview_flutter/iamport_webview_flutter.dart';
 
 class IamportCertification extends StatelessWidget {
-  final PreferredSizeWidget? appBar;
-  final Widget? initialChild;
-  final String userCode;
-  final CertificationData data;
-  final callback;
-  final Set<Factory<OneSequenceGestureRecognizer>>? gestureRecognizers;
-  final String? customUserAgent;
 
-  IamportCertification({
-    Key? key,
+  const IamportCertification({
+    super.key,
     this.appBar,
     this.initialChild,
     required this.userCode,
@@ -30,28 +23,35 @@ class IamportCertification extends StatelessWidget {
     required this.callback,
     this.gestureRecognizers,
     this.customUserAgent,
-  }) : super(key: key);
+  });
+  final PreferredSizeWidget? appBar;
+  final Widget? initialChild;
+  final String userCode;
+  final CertificationData data;
+  final ValueSetter<Map<String, String>> callback;
+  final Set<Factory<OneSequenceGestureRecognizer>>? gestureRecognizers;
+  final String? customUserAgent;
 
   @override
   Widget build(BuildContext context) {
     var redirectUrl = UrlData.redirectUrl;
-    if (this.data.mRedirectUrl != null && this.data.mRedirectUrl!.isNotEmpty) {
-      redirectUrl = this.data.mRedirectUrl!;
+    if (data.mRedirectUrl != null && data.mRedirectUrl!.isNotEmpty) {
+      redirectUrl = data.mRedirectUrl!;
     }
 
-    IamportValidation validation =
+    final validation =
         IamportValidation.fromCertificationData(userCode, data, callback);
     if (validation.getIsValid()) {
       return IamportWebView(
         type: ActionType.auth,
-        appBar: this.appBar,
-        initialChild: this.initialChild,
-        gestureRecognizers: this.gestureRecognizers,
-        customUserAgent: this.customUserAgent,
-        executeJS: (WebViewController controller) {
-          controller.evaluateJavascript('''
-            IMP.init("${this.userCode}");
-            IMP.certification(${jsonEncode(this.data.toJson())}, function(response) {
+        appBar: appBar,
+        initialChild: initialChild,
+        gestureRecognizers: gestureRecognizers,
+        customUserAgent: customUserAgent,
+        executeJS: (WebViewController controller) async {
+          await controller.evaluateJavascript('''
+            IMP.init("$userCode");
+            IMP.certification(${jsonEncode(data.toJson())}, function(response) {
               const query = [];
               Object.keys(response).forEach(function(key) {
                 query.push(key + "=" + response[key]);
@@ -60,9 +60,7 @@ class IamportCertification extends StatelessWidget {
             });
           ''');
         },
-        useQueryData: (Map<String, String> data) {
-          this.callback(data);
-        },
+        useQueryData: callback,
         isPaymentOver: (String url) {
           return url.startsWith(redirectUrl);
         },