Realm Xamarin.Android Google Auth fails with "The provided credentials are invalid or the user does not exist."

I'm building an Open-Source cross platform app for iOS and Android using Realm platform for its database and auth.

When attempting to auth with Google on iOS and then hand the id_token to Realm I can sign in. However on Android I can never get it to auth.

I have created a keystore, and a key. Signed the app in debug with this key, created the clientId from this key and then given this to the Realm Object Server. I've done this twice to check my working.

Some of the other similar issues relate to trying to register the account again on Realm. However with Google auth this does not seem to be possible and I have tried with a new blank account to no avail.

The entire project is available at GitHub.

The auth code that fails:

private static async Task<User> SetupRealmUser(Account account)
    var at = account.Properties["id_token"];
    return await User.LoginAsync(Realms.Sync.Credentials.Google(at), new Uri("https" + RealmServerUri));

Any help would be greatly appreciated, I've tried everything and can't seem to get it to work.