After updating my google play services to rev 28 i\'m getting this error. Im not sure why this is happening as it was working fine before.
here is my build.gradl
I copied the google-services.json file i downloaded and pasted it in app root folder i.e in your android studio,
google-services.json
app root
Please also make sure the 'google-services.json' file you downloaded has the same name with the one you pasted in the root directory.
This worked for me. thanks