In the Android tab, you will need to insert you Android package ID, together with the Firebase sender id, and Firebase server key.

Each Android mobile app had its own application ID, which is a unique identifier of your app on the device and in Google Store.

android

For your custom mobile app, you will need a Firebase sender ID and a Server key in order for push notifications to work. You can find them at console.firebase.google.com by selecting your project and navigating to Project Settings > Cloud Messaging.