exec ffmpeg gets no input during stream (Ubuntu 24.02)

[TyroTechSoft]

Hello!
If I send an RTMP stream via OBS:
Server: rtmp://IP/live
Key: 1234

The server receives this and it works via "push (to YouTube)".
If I use "exec ffmpeg ... (to YouTube)", ffmpeg starts, but it doesn't get a video stream.

It is working.

rtmp {
server {
listen 1935;
chunk_size 4096;
max_message 5M;
application live {
live on;
push rtmp://a.rtmp.youtube.com/live2/MyKey;
}
}
}

That does not work.

rtmp {
server {
listen 1935;
chunk_size 4096;
max_message 5M;
application live {
live on;
exec ffmpeg -i rtmp://127.0.0.1/live/OBSkey -c copy -f flv rtmp://a.rtmp.youtube.com/live2/MyKey;
}
}
}

When I use ffprobe, I don't see any video stream.

I have an old server with Ubuntu 22.04, everything works here.
Unfortunately I have to use 24.02 for the new server, otherwise I can't use the iGPU.

I don't get an error message.
When I start ffmpeg in the console, it waits for a video input.

If I stop nginx and start ffmpeg as server and listen on the port, it works.

I don't know if it's due to nginx itself or the rtmp module.

Hopefully someone can help me.
Many thanks
Regards