TestFlight: The requested app is not available or doesn't exist.

I'm getting error when I'm trying to install TestFlight I'm getting the requested app does not exist or not available error, TestFlight delivery was successful and also setup is correct, our app is still in development and we have release any version on app store yet, we are testing via TestFlight, please help to resolve this issue. I have raised many support requests as well but not getting any response