Assuming you aren’t using a Smart Controller, have you tried using a different cable between your controller and phone? I had this a few times when I tried using a (cheap) cable I brought off t’internet. Swapped to a new one, all sorted.
Also, just to clarify - when you say the image is black, do you see anything on the app (like the battery, mini-map, etc) or is the whole screen just black? The cable problem caused the latter.
Edit: Never mind… just saw your other post (DJI Smart Controller - charging issue?) 