In 2022 the PlaySignage player on Windows can't play "Live Now" webcam feeds from YouTube.
The message it gives is a bit misleading, saying "this live event is no longer available" which normally happens when the original YouTube URL has changed to a new one.
My further investigation showed that the URL works fine if you use a regular PC to go to it (Or even use the PlaySignage WebSite plugin).
It is probably related to a change YouTube seems to have made to their licensing of "Live Now" feeds. Probably to inject more advertising.
So maybe a bug, or a work around required?