sip in background flutter

Question

I have a problem when I try to pass my sip service in the background.

I'm using the flutter_background_service: ^5.0.10 plugin, I've followed the documentation scrupulously for the implementation of the service. However, I have the impression that my sip listener is garbage collected by flutter.

Here's the code for my service. I've created a service exit condition and listener with callbacks to trigger functions.

void onStart(ServiceInstance service) async {
  if (service is AndroidServiceInstance) {
    service.setForegroundNotificationInfo(
      title: "SmartDiese",
      content: "Service SIP actif",
    );
    service.setAsForegroundService();
  }

  final sipService = SipService();

  SharedPreferences preferences = await SharedPreferences.getInstance();
  String? userString = preferences.getString('user');

  if (userString != null) {
    Utilisateur user =
    Utilisateur.fromJson(jsonDecode(userString) as Map<String, dynamic>);

    UaSettings settings =
    getSettings(user: user, helper: sipService.helper, listener: sipService.listener);

    sipService.helper.start(settings);
    sipService.helper.listeners.clear();
    sipService.helper.addSipUaHelperListener(sipService.listener);
  }

  service.on('stop').listen((event) {
    service.stopSelf();
  });

  service.on('call_service').listen(
        (event) {
      String? command = event?['command'];

      if (command == "get_current_call_state") {
        CallState? state = (sipService.listener as SipListener).getCallState();

        service.invoke("current_call_state", {
          "call": state == null ? "empty" : state.state.toString(),
        });
      } else if (command == "get_identity") {
        Call? call = (sipService.listener as SipListener).getCall();

        service.invoke("call_service", {
          "command": "current_call_identity",
          "call": call == null ? "empty" : call.remote_identity.toString(),
        });
      }
    },
  );
}

When I launch the application, I get the notification that my service has been launched. Calls to services also work correctly.

Here is the code for my sip listener:

class SipListener implements SipUaHelperListener {
  Call? call;
  CallState? state;

  Call? getCall() {
    return call;
  }

  CallState? getCallState() {
    return state;
  }

  @override
  void registrationStateChanged(RegistrationState state) {}

  @override
  void callStateChanged(Call tmpCall, CallState tmpState) async {
    call = tmpCall;
    state = tmpState;
  }

  @override
  void onNewMessage(SIPMessageRequest msg) {}

  @override
  void transportStateChanged(TransportState state) {}

  @override
  void onNewNotify(Notify ntf) {}

  @override
  void onNewReinvite(ReInvite event) {}
}

My problem is that the callStateChanged method is never triggered when an incoming call arrives on the application.

Thank you in advance for your help,