Help, we have j

Help, we have just installed our doorbell camera and It is working on my phone, but my boyfriend only gets a dark screen.. he can hear the sound from outside but gets a black screen

What is the phone ?

Which doorbell model?

Sometimes the amount of data is just too much for some devices/connections to show everything correctly.
Have a look at the set streaming quality… It might help when you lower it - at least for a test.