Delivery receipt can be used to see whether a message has been successfully delivered to all the intended recipients by the Sendbird server. To mark a message as delivered when an offline group channel member receives a push notification for the message from Firebase Cloud Messaging, use the
SendbirdChat.markAsDelivered(Map<String, String>) method.
When a message is delivered to a group channel member who is online, the message is marked as delivered and other members who are online are notified of the delivery receipt through the
onDeliveryStatusUpdated() method of the channel event handler.