how to subscribe to a listener from native code in flutter

I have a class with an initialization method, inside which a listener is created, and I don't quite understand how to subscribe to this listener from the Flutter side? Always return FlutterResult?

init() {
        //self.methodChannel = methodChannel
        LoggingService.Instance.logLevel = LogLevel.Debug
                
        try? mCore = Factory.Instance.createCore(configPath: "", factoryConfigPath: "", systemContext: nil)
        try? mCore.start()
        
        //Listeners
        mRegistrationDelegate = CoreDelegateStub(onAccountRegistrationStateChanged: { (core: Core, account: Account, state: RegistrationState, message: String) in
                    NSLog("New registration state is \(state) for user id \( String(describing: account.params?.identityAddress?.asString()))\n")
                    if (state == .Ok) {
                        self.loggedIn = true
                    } else if (state == .Cleared) {
                        self.loggedIn = false
                    }
                })
        mCore.addDelegate(delegate: mRegistrationDelegate)

    }

Here's an example that demonstrates how to achieve that:

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  static const platform = const MethodChannel('your_channel_name');

  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  bool loggedIn = false;

  // Subscribe to the listener in your native code
  void subscribeToListener() async {
    try {
      await MyApp.platform.invokeMethod('subscribeToListener');
    } catch (e) {
      print('Error subscribing to listener: $e');
    }
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Listener Example'),
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              ElevatedButton(
                onPressed: subscribeToListener,
                child: Text('Subscribe to Listener'),
              ),
              SizedBox(height: 20),
              Text('Logged In: ${loggedIn ? 'Yes' : 'No'}'),
            ],
          ),
        ),
      ),
    );
  }
}