classpath 'com.google.gms:google-services:4.0.1'

implementation 'com.google.firebase:firebase-core:16.0.9'

> The library com.google.firebase:firebase-iid is being requested by various other libraries at [[18.0.0,18.0.0]], but resolves to 17.1.2. Disable the plugin and check your dependencies tree using ./gradlew :app:dependencies.