* [Android specific options](https://firebase.google.com/docs/reference/fcm/rest/v1/projects.messages#AndroidNotification) * [APN(iOS) specific options](https://firebase.google.com/docs/reference/fcm/rest/v1/projects.messages#apnsconfig) * Apple Develpoers documentation: [Link1](https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server/sending_notification_requests_to_apns), [Link2](https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server/generating_a_remote_notification)
