What is the multicast_id in Firebase cloud messaging service?
As mentioned in the documentation that is provided by Google, multicast id is the unique number that identifies the multicast message.
I read it, but I did not understand it clearly. Can anyone explain it?
Per Firebase Cloud Messaging HTTP Protocol documentation:
The multicast_id is a required parameter in the FCM response payload, and is a unique ID that identifies the multicast message.
A multicast message is a notification that will be sent from a server and targeting multiple client applications.
To answer your question directly, this response parameter is just an identification ID of a multicast message sent to client applications.
I'm not sure yet, but looking at the Build App Server Send Requests documentation, you will only get this response parameter when you use Single Device Messaging targeting a single or array of registration tokens.
I hope this helps.
On a simpler note, a multicast_id is similar (if not identical enough) to a message_id.
In addition to looptheloop88's answer, the usual purpose of both the message_id and multicast_id is for tracking/logging. As I mentioned here:
There is currently no available API to make use of the
message_ids/multicast_idsto retrieve the details of the delivery status of the message sent, other than using the FCM Diagnostics Page.
