After finished your steps “here”
- Go to the “Google firebase” and “choose your project”.
- Choose the “Android” icon.
- From the “Project Overview”, choose “Project settings”.
- Choose “Cloud Messaging”, and copy the “Server Key” in the Theme option Settings page / Mobile APP / Notifications / Activate it and past the key in the input.
- Theme option settings page > Mobile APP > Notifications > Enable or disable push notifications > ON and add your key.