We are migrating from GCM to FCM in one of our projects. One of our clients asked us "Like GCM has 100 notification limit" Do we have any limitation for FCM.
Can we use the same sender-id and key for multiple environments like Dev/QA/UAT and also production?
Thanks in advance
As far as usage limitation goes, FCM is pretty much the same with GCM. See my answer here and here.
When you migrate your Google Project to Firebase, it would still retain the Sender ID. Where it is used depends entirely if it's compatible to it.