I have 5 sonos Speakers and a Spotify Premium account. I am using spotify on my Android (Pie) phone and Mac OS computer.
On both devices listed above, I can play Spotify music on my Sonos speaker (called Lounge) when I use the Sonos App. But if I use the Spotify App, the speaker called Lounge does not show up. The other 4 speakers show up fine.
I have restarted speaker, computer, check for upgrades on all devices, etc.