Google Cloud Functions: Call route from within client

I had already read this excellent answer: Do Google Cloud Platform HTTP Functions Support Route Parameters? for the server side

However there is no indication how to call a route from within Flutter app.

My current (not working) attempt in Flutter (client side):

import 'package:cloud_functions/cloud_functions.dart';
//...

Future<Null> callGoogleCloudFunctions() async {
    FirebaseFunctions functions = FirebaseFunctions.instance;
    try {
      HttpsCallable callable = functions.httpsCallable('routes/fruits');
      final results = await callable.call();
      final fruits = results.data;  // ["Apple", "Banana", "Cherry", "Date", "Fig", "Grapes"]
      print(fruits);
    } catch (e) {
      print('caught exception $e');

    }
  }

On server side (google cloud functions):

const app = express();
app.use(bodyParser.json());
app.use(cors({ origin: true }));

// configure the routes that the app will handle.
routesConfig(app)

export const routes = functions.https.onRequest(app);

export function routesConfig(app: Application) {
        app.get('/fruits', [
       fruits
   ]);

export async function fruits(req: Request, res: Response) {
   try {
         console.log("Hello logs!", {structuredData: true});
       return res.status(200).send({"fruits": ["Apple", "Banana", "Cherry", "Date", "Fig", "Grapes"] })
   } catch (err) {
       return handleError(res, err)
   }
}

NB: I have user authentification but simplified the code for MRE

With Postman I have no trouble to call https://us-central1-{{PROJECT_ID}}.cloudfunctions.net/route/fruits and get the returned string so I know my problem is only on the client side

I don't want to use http post / get functions because cloud function is very convenient when it comes to authentication:

The request to the Cloud Functions backend made by this method automatically includes a Firebase Instance ID token to identify the app instance. If a user is logged in with Firebase Auth, an auth ID token for the user is also automatically included.

Edit: Just succeeded using http package... still curious about the google cloud function plugin?