Unity Google Play 游戏插件 v11.01 授权码（令牌）为空

问：

成功登录帐户后，我正在尝试获取后端的授权令牌。但它总是空的。是否缺少一些代码，或者可能是 sha-1 指纹或其他东西？

private void Start()
{
    PlayGamesPlatform.Activate();
    LoginGooglePlayGames();
}

private void LoginGooglePlayGames()
{
    PlayGamesPlatform.Instance.Authenticate((success) =>
    {
        if (success == SignInStatus.Success)
        {
            Debug.Log("Login with Google Play games successful.");

            PlayGamesPlatform.Instance.RequestServerSideAccess(true, code =>
            {
                Debug.Log("Authorization code: " + code);
                Token = code;
                OnGetAuthToken?.Invoke(code);
            });
        }
        else
        {

            Debug.Log("Failed to retrieve Google play games authorization code");
        }
    });
}