Video trouble

Hi! Although my camera seems to be on-been through the settings so many times-and I can share screen without any problems, my students can't see me, they can only see a black screen or, if I turn the camera off, my photo. The camera works just fine, checked it with another app. I tried to delete the zoom app and install it again, but it didn't make any difference. I might have pressed something accidentally, but I really don't know what else to do to fix it...