This is interesting. It sounds like Facebook is potentially looking under the couches, so-to-speak, for spare change by doing this. I also wonder if other comms apps are going to be doing this too?
In UI: https://cs.joshstrange.com/zTpdlC
End of call, always on top, popup: https://cs.joshstrange.com/BizVwE
EDIT: I get that it's less offensive since it's a "first-party ad"/"upsell" and I could forgive the banner in the app (even though dismissing it only makes it go away for like 24 hours, if that) but the popups post-meeting drive me bonkers. To the point I've considered seeing if I can write some code to watch for that window and kill it right away.
Paying customer? That's big no no