Flutter FirebaseFirestore multiple apps

Im working on a flutter project, when i'm trying to connect to Firestore using a secondary firebase app. see Configure multiple projects.

I get the following error when trying to connect to db

secAppFirestore
        .collection("yos")

:

"Unhandled Exception: [core/no-app] No Firebase App '[DEFAULT]' has been created - call Firebase.initializeApp".

my code

void main() async {
  // Avoid errors caused by flutter upgrade.
  WidgetsFlutterBinding.ensureInitialized();

  await Firebase.initializeApp(
    name: "yostest2-xxxxx",
    options: FirebaseOptions(
      apiKey: "AIzaSy...",
      appId: "1:68080...",
      messagingSenderId: "",
      projectId: "yostest2-xxxxx",
      storageBucket: "yostest2-xxxxx.appspot.com",
      databaseURL: 'https://yostest2-xxxxx.firebaseio.com',
    ),
  );

  runApp(const MyApp());
}

....

 void _incrementCounter() async {
    FirebaseApp secondaryApp = Firebase.app('yostest2-xxxxx');
    FirebaseFirestore secAppFirestore =
        FirebaseFirestore.instanceFor(app: secondaryApp);
    await secAppFirestore
        .collection("yos")
        .add({"timestamp": FieldValue.serverTimestamp()});

    setState(() {
      _counter++;
    });
  }