I am Assuming you have created / configured
- Keystore file to sign apk
- Google Cloud Project and OAuth Credentials for your android App
If not then you can find it here:
https://medium.com/@edigleyssonsilva/adding-google-sign-in-to-your-ionic-3-4-5-app-8ed81744e8ba
Step 1
When installing plugin make sure you provide correct variables.
- For REVERSED_CLIENT_ID make sure to provide the Credentials you generated for Android application.
- For WEB_APPLICATION_CLIENT_ID make sure to provide Credentials you generated for Web Application.
ionic cordova plugin add cordova-plugin-googleplus --variable REVERSED_CLIENT_ID=com.googleusercontent.apps.<id> --variable WEB_APPLICATION_CLIENT_ID=web_application_client_id.apps.googleusercontent.com

Step 2
Once plugin is installed Remove Platform and Add again. Then Create a Production Release and sign it. It will work on Production release and error should go away. However when debugging the application in mobile you will still see the error 10. In order to resolve this you have to create a file called debug-signing.properties
inside platforms/android
put the following contents:
keyAlias=alias_name keyPassword=000100010 storeFile=myapp.keystore storePassword=000100010
Once you have created this file put your generated keystore in same folder. That’s basically it! Now when you debug the app it will still work.