Hi.
i am having the same problem with my iPhone 7 Plus..
and i know of another person that is having the same problem also with an iPhone 7 Plus.
my real camera works great on any app but my front facing câmera only works on the iPhone câmera app..
on FaceTime i cannot answer calls, the iPhone ends the call as soon as i press the button to answer the call (vídeo)
on the Facebook Messenger app my front câmera just shows a Black screen...
it is not a front camera problem because, as i said, the front câmera works on the iPhone câmera app.. i can take selfies, no problem..
but on every other app the front camera does not work.. and that includes FaceTime..
this started happening after an IOS update.. last week was able to video-chat on facetime,.. since then i updated the phone and FaceTime is not working anymore..
this is a software issue that is affecting the iPhone 7 Plus..
the person i know that also has an iPhone 7 Plus with the same problem, it all started after an IOS update too..
i also have an iPhone 7 and that was not affected.. it seems it is just the iPhone 7 plus