Camera issues

My camera shows a black screen when I join an external meeting.  I can see myself before joining fine and as soon as the host accepts me in the screen is black. Audio is fine.

The same issue has happened on two different lap tops so not a Lenovo issue as the other one is HP.

It's absolutely fine if I create the meeting invite though myself and a guest joins my meeting.  Only not working when I join as a guest to another meeting.  I assume a setting somewhere but I can't find this at all. Any ideas?