Firebase Flutter upgrade problem to version ^8.0.0-dev.15

[esdan7]

Hello,

I have upgraded firebase from ^7.0.0 to ^8.0.0-dev.15 and now I am getting errors, that I am not sure how to fix.
Here is my legacy working code:

void initFirebase() {
    _firebaseMessaging.configure(
      onMessage: (Map<String, dynamic> message) async {
        print("onMessage: $message");
      },
      onLaunch: (Map<String, dynamic> message) async {
        print("onLaunch: $message");
      },
      onResume: (Map<String, dynamic> message) async {
        print("onResume: $message");
      },
    );
    _firebaseMessaging.requestNotificationPermissions(
        const IosNotificationSettings(
            sound: true, badge: true, alert: true, provisional: true));
    _firebaseMessaging.onIosSettingsRegistered
        .listen((IosNotificationSettings settings) {});
    _firebaseMessaging.getToken().then((String token) {
      assert(token != null);
      setState(() {
        _notificationToken = token;
      });
    });
  }

Now, I started fixing the code as per the official documentation but cannot get it entirely right, will appreciate if someone can help out:

  void initFirebase() {
    FirebaseMessaging.onMessage.listen(
      (RemoteMessage message) {
        print("onMessage: $message");
      });
      FirebaseMessaging.onMessageOpenedApp.listen(
      (RemoteMessage message) {
        print("onMessageOpenedApp: $message");
      });
    
    NotificationSettings settings = messaging.requestPermission (
        sound: true, badge: true, alert: true, provisional: true,
    );
    _firebaseMessaging.onIosSettingsRegistered
        .listen((IosNotificationSettings settings) {});
    _firebaseMessaging.getToken().then((String token) {
      assert(token != null);
      setState(() {
        _notificationToken = token;
      });
    });
  }

[esdan7]

@Salakar, would you be able to have a look on this issue please? I am stuck with this code upgrade for several days now. I posted the question here and on Stackoverflow but either no one knows how to do it or they can't be bothered to reply. I would really appreciate your advice as the expert in flutterfire.