Google Sign-In for Android with a backend server

I need to set up Google registration in my application. The first thing I did was read the documentation , then doing all of the above 4 times, I can’t get a successful answer from GoogleSignInResult . The code was taken from the example , and it works with a simple request, such as .requestEmail() , but with .requestIdToken(getString(R.string.server_client_id)) does not work. I want to clarify! When creating Credential, I used a non-existing address, that is, there is no server yet! Could it be because there is no server? I thought that at first the token is generated based on server_client_id , and only then there is a connection with the server. And, if possible, please give a link to a good OAuth article. I found it in the original, but it's still hard for me to read everything in the original, thanks.