Enable Cloud Services feature from Essential Kit Settings
If you are NOT planning to use Game Services along with Cloud Services, you still need to fill the Play Services Application Id entry in Game Services settings (and can disable it). This is because, on Android, Cloud services is internally dependent on Google play services.
Enabling Synchronize on load, on Android, may open google play services login if user isn't logged at-least once. So, it's good to call first Synchronize call as per your game requirements.