It seems that the fcm API allows sending to multiple tokens via sendToDevice and sendMulticast. sendToDevice is a legacy call? Should we use sendMulticast instead?
https://firebase.google.com/docs/reference/admin/node/admin.messaging.Messaging#sendtodevice https://firebase.google.com/docs/reference/admin/node/admin.messaging.Messaging#sendmulticast
"sendMulticast" returns Promise for BatchResponse whereas "sendToDevice" returns Promise for MessagingDevicesResponse
From https://firebase.google.com/docs/cloud-messaging/send-message#adminSDK-legacy-send-methods regarding "sendMulticast":
For Firebase Admin SDKs, this operation uses the sendAll() API under the hood, as shown in the examples. The return value is a BatchResponse whose responses list corresponds to the order of the input tokens. This is useful when you want to check which tokens resulted in errors.
