IOS: when you call Isolate.spawn, Error occur

[spysoos]

call Isolate.spawn inner "onStart" function, you will get An error

  WidgetsFlutterBinding.ensureInitialized();
  FlutterBackgroundService.initialize(onStart);
  runApp(MyApp());
}

void onStart() {
  WidgetsFlutterBinding.ensureInitialized();

  var _mainReceiverPort = ReceivePort();
  Isolate.spawn(_sendSub, _mainReceiverPort.sendPort);
}```