Migrate a GCM Client App for Android to Firebase Cloud Messaging
As of April 10, 2018, Google has deprecated GCM. The GCM server and client APIs are deprecated and will be removed as soon as April 11, 2019. Migrate GCM apps to Firebase Cloud Messaging (FCM), which inherits the reliable and scalable GCM infrastructure, plus many new features. See the migration guide to learn more.
https://android.googleapis.com/gcm/send -> https://fcm.googleapis.com/fcm/send