"airplay device cannot be selected for audio output"

I've been using airplay from my MacBook pro retina (early 2015) (on OS 10.14.6) to my Apple TV (3rd Gen A1469) for a long time now. But last night when I tried to airplay from iTunes, I got the message in the subject, "airplay device cannot be selected for audio output". When I went to safari and tried to simply mirror the screen to the Apple TV, I could, but as I chose a video to play, it wouldn't allow the video to play, which is something I had just done the week before. I can't think of anything different I've done or modified that would change anything. I restarted the Apple TV and my computer, hoping things would 'remember' how to talk to each other, and no luck.

I just now changed my network (my Cox router comes with two networks) and I got a YouTube video Airplay and to mirror and play. But I couldn't get a Disney+ video to mirror and play (I get an error), and I couldn't get an iTunes video to airplay. ...but funny, as it connected at first it was ONLY playing the audio, not the video. But then when it didn't successfully connect it told me again the same message "airplay device cannot be selected for audio output". ...hmmm.

Please advise.