AndroidMessagePriority enum

Default priority for data messages. Normal priority messages won't open network connections on a sleeping device, and their delivery may be delayed to conserve the battery. For less time-sensitive messages, such as notifications of new email or other data to sync, choose normal delivery priority.

Default priority for notification messages. FCM attempts to deliver high priority messages immediately, allowing the FCM service to wake a sleeping device when possible and open a network connection to your app server. Apps with instant messaging, chat, or voice call alerts, for example, generally need to open a network connection and make sure FCM delivers the message to the device without delay. Set high priority if the message is time-critical and requires the user's immediate interaction, but beware that setting your messages to high priority contributes more to battery drain compared with normal priority messages.