Targets, options, and payload for downstream HTTP messages (JSON).
https://firebase.google.com/docs/cloud-messaging/http-server-ref#table1
This parameter specifies the custom key-value pairs of the message's payload.
This parameter specifies a list of devices (registration tokens, or IDs) receiving a multicast message. It must contain at least 1 and at most 1000 registration tokens.
See Implementation
Targets, options, and payload for downstream HTTP messages (JSON).
https://firebase.google.com/docs/cloud-messaging/http-server-ref#table1