I figured this out. Monterrey has Airplay Receiver listening on Port 5000. You can disable it in System Preferences => Sharing => AirPlay Receiver. Here is more info. https://developer.apple.com/forums/thread/682332

I'm developing locally using Postman and Jetbrains Rider IDE and am getting this also. HTTP/1.1 403 Forbidden Content-Length: 0 Server: AirTunes/566.30.1 I haven't found a resolution. It seems to happen intermittently. I'm going to update the OS with the latest update and try again.