JJRC X12 / Ex4 Connection Problem after Camera change

Good day

I signed up here today because I need help with a problem.
I bought the JJRC X12 drone and flew well with it the first few times, but then I crashed the drone against the wall of my house.
After that, however, the image from the drone was blurred.
The video recording was also out of focus, the drone’s camera probably has a defect.
After a few searches, I ordered the complete camera from China, but for the EX 4 (which should actually be identical).
I then rebuilt the camera and started the drone again.
From then on I had the problem that the drone only glows blue and, according to the APP, no connection between the drone and the remote control is established.
If I remove the connection cable between the camera and the drone, the drone lights up green after starting and I have a connection between the drone and the remote control, but unfortunately no picture.
I then reinstalled the older blurry camera and restarted the drone, but it was the same error.
I can’t get a connection between the drone and the remote control.
That’s what the APP tells me.
Who might have a tip for me about what else I can do?
Many thanks