Chomecast audio isn't in Spotify Connect list

[Preckie]

I am trying to play music from my Spotify (on Samsung S7), but Chromecast Audio won't appear on the Spotify Connect list! I have already set up 2 of these before. It used to work randomly.. and when it does, it stutters. Now, both can't be seen anymore. I can cast using the Google Home app to the Chromecast Audio just fine, but not from the Spotify app directly. 

The rest of my network-connected devices work flawlessly: 2 Onkyo receivers, a Sony Android TV, Sony PS4. Only this device won't work and Chromecast has implied that the problem is on Spotify's end.

Any suggestions?