Project have just this code, and I just follow this description. Visit https://developers.google.com/games/services/android/init
Make Project and adding library \'go
It seems like you forget to add APP_ID metadata in your manifest file. You need to add the following code exactly inside the tag in the Android Manifest file:
<meta-data android:name="com.google.android.gms.games.APP_ID"
android:value="@string/app_id" />
Please make sure the meta tag is not inside the tag but tag, and use APP_ID which is 12 digits number placed right of your game title in your play game console.
for more info, check below link: https://developers.google.com/games/services/android/quickstart#step_3_modify_your_code