Sonos Voice Control currently only supports Sonos Radio, Apple Music, Amazon Music, Deezer, and Pandora. But you should be able to use Spotify with Google Assistant on Sonos. Have you added Spotify as a music service and set up Google Assistant in the Sonos app?

Read more here:

https://support.sonos.com/s/article/2757

https://support.sonos.com/s/article/3467

Note that Google requires that when Google Assistant is installed, there can be no other voice assistant.