Airplay won't connect to Sonos One

Why won't Airplay connect to my Sonos One speakers? This is the error I get: "An unknown error occurred (-15007)."

It won't work from my macbook air, my iphone, or my wife's similar apple products. The Sonos speakers do appear as an option, but when I try to connect to them, using Airplay, I get this error.

The reason I'm trying to do this is because I want to play the audio from apps like Youtube and Netllix to the speakers. The Sonos app only plays music from audio-only apps like Spotify. To play the audio from other sources, like once with video, on Sonos speakers that are set to stereo, you have to use Airplay. But I can't get airplay to connect.

Any help is welcome. This is driving me crazy! Thanks.