File google-services.json is missing from module root folder. The Google Services Plugin cannot function without it

1. Go to firebase console

2. Create a new project.

3. Then go and click on Add Firebase to your Android app

4. Add Package name (from AndroidManifest.xml)

5. Then it'll generate google-services.json

6. Copy this file and add it to (i) your project root (ii) your project>app

7. Sync project (Tools -> Android -> Sync Project with Gradle Files)

Hope this will help to you :)