It worked for me, I’ll copy from my thing and see if this works?
https://www.inthematrixxx.com/podcast/flynndication/
Perhaps it has to do with the 'podcast' protocol. That link does not work but if I go to https://www.inthematrixxx.com and see their podcasts, 'flynndication' comes up and I can play it ... the url still reads just as you posted it, but it does not work except as I described. Who knows? :^)