This is a bit complicated:

I have tried several times to link my Sonos One speaker pair to Google Assistant. I’ve tried in a couple of different ways: From the SONOS App, and when that failed from my google home app. In both cases I eventually ran into a notification screen stating I need to register my speakers. As far as I remember my speakers are registered, and the app and speakers are working fine. I followed the directions that popped up, stating to go to account settings to register speakers, and that if I cannot I need to perform an update. I went to account settings and did not find a way to register my speakers, so I attempted an update but the app is already up to date.