Source: Life of a message from FCM to the device from Firebase
If you are a user of Firebase Cloud Messaging (FCM), you know that there are many different ways to send messages. You can target an application on a device, or target millions of them through the topics API. FCM APIs tell you if there was a failure during the acceptance of the request by returning an error code and an explanation for the failure, but this only covers the part of the request between you and the FCM backend. What happens after FCM accepts your message request?
In this post, we will look into the Firebase Cloud Messaging infrastructure and how messages are actually delivered to devices.
When FCM returns a successful response to your API request, it simply means that FCM will start trying to deliver this message to the device or to the service responsible for delivering the message to the device (for example: Apple Push Notification service for delivery to iOS devices or Mozilla Push Service for delivery to Firefox browsers). It will try this until:
Note: If the time to live of the pending messages has expired, the above functions will not be triggered.
There are many factors that affect the actual delivery of the message to the device and the amount of information FCM can provide about the delivery.
Note: If you’d like to analyze message delivery events for your project, you can do so by exporting FCM data into BigQuery.
On iOS, there are two ways in which FCM can send a message to a device:
Note: If you’d like to access iOS notification delivery information for display notifications, you can use the FCM Reporting Dashboard. This dashboard leverages Google Analytics for Firebase data sharing features to collect delivery information through Firebase Android and iOS SDKs for display notifications.