I have been following this tutorial to get Google SignOn going: https://developers.google.com/identity/sign-in/android/start-integrating
When I run my application lo
You are probably missing dev console registration. It's very common developers will have multiple signing cert configuration: debug key store, test environment signing cert, production signing cert. signing cert SHA1 + package name uniquely identifies an Android client and needs to be registered individually in dev console.
See below blogpost to understand more about OAuth clients registration:
http://android-developers.blogspot.com/2016/03/registering-oauth-clients-for-google.html
Or see this post: Test google signin on Android in development phase