[Solved] Flutter : [core/not-initialized] Firebase has not been correctly initialized. Have you added the “google-services.json” file to the project?

Problem

I’ve connected my Flutter app to Firebase by adding the SHA1 key ( How to Get SHA-1 key in Android Studio for Firebase. ) and package name in the Firebase console, and also downloaded and provided google-service.json in my Flutter app at android/app. But when I run the app it’s Showing an error that I’ve not provided google-service.json a file in my app. The Error Says –

E/flutter (15568): [ERROR:flutter/lib/ui/ui_dart_state.cc(166)] Unhandled Exception: [core/not-initialized] Firebase has not been correctly initialized. Have you added the "google-services.json" file to the project? 
E/flutter (15568): 

Solution

After hours of struggle, I am able to figure out the solution.

First, add the ‘google-services.json‘ plugin as a dependency inside of the Android/build.gradle file:

2. Lastly, execute the plugin by adding the following underneath the line apply plugin:
add after ‘com.android.application’, within the /android/app/build.gradle file:

apply plugin: ‘com.google.gms.google-services