Facebook is constantly changing things so that developers can not do live streaming on mobile devices. The workaround is the following:

Go to the "Advanced" setting after you select the "Facebook" service and then tap "Reset Values". This will populate the latest GO LIVE LINK and USER AGENT STRING.

And here is the latest information for Facebook: https://scorecam.pydmsw.com/livestreaming/facebook.html

Please read very carefully as all the latest answers are there.

Update: Easiest solution to connect to Facebook Live is to use a service like Restream or Castr.