Here’s a very good lesson to all other DJs as well: if your event is started despite the video not working, it’s 100% on you.
There is a preview screen (which very explicitly and with bold letters states that if the preview isn’t working, your event wideo will also not work) that is meant to catch any possible errors, like here when the DJ forgot to update his event video URL after the streaming keys had changed.
If you have any doubts about new settings ot whatever changes you have made, just fire up a quick private test event to see if everything is working as expected. And remember to leave plenty of time (preferably 30 mins) for warmup so that you and your audience are ready at the scheduled starting time 