The legacy Firebase Cloud Messaging API server key is no longer accepted for configuring Android push notifications on mobile connected apps. Because of a change in how Google handles push notifications, Android mobile connected apps now require the Admin SDK private key and project ID from a Google Firebase project.
Where: This change applies to mobile connected apps with Android push notifications. Connected apps can be created in Group, Professional, Enterprise, Essentials, Performance, Unlimited, and Developer editions.
How: Get the required information from your Firebase project in the Google Firebase Console. Then submit the information to your mobile connected app’s settings in App Manager.