Google Services Plugin cannot function without google-services.json

You are using Google signin right? So u definitely need a google-services.json file

Refer this link

Add the dependency to your project-level build.gradle:

classpath ''

Add the plugin to your app-level build.gradle:

apply plugin: ''

When you add apply plugin: '' inside your app-level build.gradle it parses configuration information from the google-services.json file.

You removed google-services.json file, that's why it is not able to parse
So remove the below line too from your app-level build.gradle who triggered parsing to make it work again.

apply plugin: ''