As of April 10, 2018, Google has deprecated GCM(Google Cloud Messaging) and migrating to FCM(Firebase Cloud Messaging), which inherits the reliable and scalable GCM infrastructure, plus many new features. The GCM server and client APIs are deprecated and will be removed as soon as April 11, 2019.
GCM is used for receiving Push Notifications on your Android Mobile App.
So, if your Support Period is active, then open a support ticket to request for migrating the certificate to FCM(Firebase Cloud Messaging) from here: https://www.socialenginesolutions.com/support/
If your Support Plan is expired, then you can purchase our support plans from here:- https://www.socialenginesolutions.com/support-mobile-apps-subscriptions/
Or purchase our One Time Support from here:- https://www.socialenginesolutions.com/social-engine/one-month-support-service/