The Sonos apps do not appear to support YouTube Channels properly. I have two channels; the first is my "primary" channel, that I use for video playlists, the other is one I created for music playlists. This is a very common approach for keeping video and music playlists separate.
I can add each of these channels to the Sonos app's Music Services, but I only see my playlists and content from my "primary" channel. Content from the channel I use for music is blank.
Very frustrating
