Adding Google Play Games Services to my game sucked. A basic feature that should take no time at all ended up taking a rather frustrating day. Part of that frustration is that you need to test on a device (or possibly on an emulator). Google Play Games Services does not work in the Unity editor and likely does not work on other 3rd party platforms.
Verify Your Account is Setup
If you’ve already done all the set-up, make sure your account is prepared. If you don’t usually use games services, you may not have an account prepared.
Full Process to Support Google Play Games Services
1) Fully prepare your app and games services, so they’re ready to publish.
2) When setting the signing-certificate fingerprint, use the Upload Certificate, not App Signing Certificate. (You can find both in the Release Management -> App Signing section. If you used the wrong certificate, you can change it in the Google API -> Credentials settings.)
3) (On Unity) Install the plugin and follow the directions. Don’t fill out Web App Client Id (unless you have a custom backend). Then test everything with the example script and build your ideal set-up using the documentation.
Once you get used to the process, the Google Play Games Services implementation process is fairly straightforward, but it can be incredibly frustrating without knowing the tricks.
I hope you found this article helpful. If you have any extra issues or tips, leave them in the comments and I’ll check them out.