Flutter Firebase Notification on Web - flutter

Question

In my flutter project, I already have notifications set up using firebase_messaging for Android and iOS. I am trying to add the same for Web. I had tried it before (mostly changing index.html with firebase-configs and initializing), but it had not worked then and I had left it. Now their document asks to use the new way, which asks only to configure it in the dart-files, and talks nothing about doing anything on index or other js files. So I have removed imports, and initialization from index.html, and not added any other file ( I have tried adding empty firebase-messaging-sw.js and removing it). This is the error I am getting:
[firebase_messaging/failed-service-worker-registration] Messaging: We are unable to register the default service worker. Failed to register a ServiceWorker for scope ('http://localhost:44055/firebase-cloud-messaging-push-scope') with script ('http://localhost:44055/firebase-messaging-sw.js'): A bad HTTP response code (404) was received when fetching the script. .
What am I missing? Are those steps incomplete? I also tried the steps in this article , but still have the same issues.
Edit
These are all the code-parts related to firebase-messaging.
await Firebase.initializeApp(
options: DefaultFirebaseOptions.currentPlatform,
);
firebaseAnalytics = FirebaseAnalytics.instance;
firebaseMessaging = FirebaseMessaging.instance; //
final notificationSettings = await firebaseMessaging.requestPermission();
debugPrint('User granted permission: ${notificationSettings.authorizationStatus}');
if (!kIsWeb) {
FirebaseMessaging.onBackgroundMessage(
_firebaseMessagingBackgroundHandler);
channel = const AndroidNotificationChannel(
'high_importance_channel', // id
'High Importance Notifications', // title
description: 'This channel is used for important notifications.',
// description
importance: Importance.max,
);
flutterLocalNotificationsPlugin = FlutterLocalNotificationsPlugin();
/// Create an Android Notification Channel.
///
/// We use this channel in the `AndroidManifest.xml` file to override the
/// default FCM channel to enable heads up notifications.
await flutterLocalNotificationsPlugin
.resolvePlatformSpecificImplementation<
AndroidFlutterLocalNotificationsPlugin>()
?.createNotificationChannel(channel);
/// Update the iOS foreground notification presentation options to allow
/// heads up notifications.
await FirebaseMessaging.instance
.setForegroundNotificationPresentationOptions(
alert: true,
badge: true,
sound: true,
);
}
.
.
.
.
.
.
.
.
if (kIsWeb) {
// this is where the code throws error:
token = (await firebaseMessaging.getToken(
vapidKey: "BLn....pH8",
))!;
} else {
token = (await firebaseMessaging.getToken())!;
}