Hmmmm. Worked beautifully for an hour then stopped! At present can see all the Sonos speakers from Spotify but can't connect to them. Probably something obvious but beats me at the moment.
https://www.engadget.com/2016/12/06/all-sonos-owners-can-now-use-spotify-to-control-their-speakers/
From today you can now sit in the Spotify app and direct your music to your Sonos speakers. Sounds like a small change, but it's very good. Get updating your apps.
Apols if fixtures but...