Quickblox chat push notifications are not working after migrating from GCM to FCM (v20.1.0)

[Dev1535]

1. We have migrated the code from GCM to FCM by following the steps provided by the quickblox (https://quickblox.com/developers/How_to_migrate_from_GCM_to_FCM).
2. Also, we have updated the Quickblox - v3.9.1 version as part of the migration to access Firebase classes.
   3.After successful migration, we have verified and found that Chat Notifications are displayed in Quickblox admin console push notifications queue with sent status, However, Notifications are not being sent to devices even after a couple of days.
   4.Currently, we are using the quickblox basic plan, is there any restriction for basic plan to send/receive chat push notifications to devices?
3. Do we need to configure anything extra to send notifications to the devices?