Android app does not connect to Firebase

I had the exact same issue. I built successfully but got the same message when hitting the 'Connect to Firebase' button via Assistant.

It turned out that I had a warning that I had to fix to get it to work.

"Configuration on demand is an incubating feature. WARNING: Configuration 'compile' is obsolete and has been replaced with 'implementation' and 'api'. It will be removed at the end of 2018. For more information see: http://d.android.com/r/tools/update-dependency-configurations.html"

I just had to replace my 'compile's with 'api' and then it worked. I'd suggest looking into fixing warnings if you have any even though your build is successful.

I tried a lot of ways, but the simplest way is updated com.google.gms:google-services from 3.1.1 to 3.2.0