How to find your firebase server key - andrehtissot/cordova-plugin-firebase-extended-notification-app-example GitHub Wiki
- Access https://console.firebase.google.com/
- Click on your firebase project, the same one that you got the "google-services.json".
- Click on the three dots as illustrated below.
- Click on the "Settings" option.
- Click on "CLOUD MESSAGING".
- Now copy the code beside "Server key".
- Enjoy.