The short version, then the thing that catches people out.
rtmps://live-api-s.facebook.com:443/rtmp/
Without Persistent stream key switched on, Facebook issues a new key for every broadcast, so a looping channel stops working the moment the first one ends. Turn it on before you copy anything.
Facebook uses RTMPS rather than RTMP. Beamd fills in the right address automatically, which is a common source of "connection refused" when it is typed by hand.
Your key is stored encrypted and is never shown back to you, on screen or in email.
Stream 24/7 with your computer off