From your Firebase console, go to the Project Settings > Service Accounts Tab. You need to download your service account information.
Firebase Admin SDK > Node.js > Generate new private key and a JSON file will be downloaded.
Open that JSON file in any text editor and copy the information inside the {} curly bracket.
Now go to your IDE and open lib/configs/fcm_config.dart the file and paste the text you have just copied inside the curly bracket. That's it.
