No Signal in the Spout Sender Window if I use the webcam

Hey, I managed to run everything except if I try to capture the signal from my webcam with opencv and then send it. Then I just get a black screen. I tried to change the resolution and also use the right webcam ID. With cv.imshow(x, frame) I can see the livestream, but in the Spout Sender Window it is just black. Maybe someone can help me.

Thanks a lot!