Lock down IPs to Firebase Cloud Messaging (FCM)

I need to set up push notification for Android, and one of the requirement is to allow 443 traffic to Firebase Cloud Messaging (FCM). However, my info sec refused to open the entire block and wants to limit specific IPs or scopes only. Any suggestion? I've searched high and dry without any luck.

https://stackoverflow.com/questions/...s-for-firewall

Thanks Rodney.

But the below did say outbound 443 must be open to Firebase Cloud Messaging (FCM). Is that no longer necessary?

BlackBerry Push Notifications - BlackBerry Enterprise Mobility Server - 2.6

Originally Posted by tchenggeller

But the below did say outbound 443 must be open to Firebase Cloud Messaging (FCM). Is that no longer necessary?

BlackBerry Push Notifications - BlackBerry Enterprise Mobility Server - 2.6

It is noted that you should whitelist the IPs on Google's ASN as mentioned
To help, here is link to their ASN

https://ipinfo.io/AS15169

We can't white list all the IPs as mentioned. For now, we only allow port port 5228 to https://fcm.googleapis.com/fcm/send from my BEMS.

Support also shares the link below.

When BlackBerry Work is put in the background, it does not receive push notifications for new emails to Android devices.