Cannot change dependencies of configuration \':app:api\' after it has been included in dependency resolution.
I was also getting the same error. Thanks to @Dominik for linking to the duplicate issue.
For now the work around is to downgrade com.google.gms:google-services
to version 3.2.1
while the Android team works on a fix.
For today you can use
classpath 'com.google.gms:google-services:4.0.2'
Seems it works.