As it is stated by Google, GCM API will be deprecated by April 11 2019. I could not see any documentation (All documents are related with GCM and some implementation which are deprecated) or roadmap about this integration. Can anyone please send an information about it?
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.