I see that a lot of people here and on other forums have problems with activating Google Assistant on Sonos. When I first setup my system there was no problem adding it to Sonos Roam. But after some problems where I had to reset my system Google Assistant couldn’t find Sonos Roam again when I tried to add it.

This is how I managed to add it back again.

1. Open Google Home on your phone (I run iOS, might be different on an Android).
2. Click Settings.
3. Scroll down to the bottom and click Works with Google.
4. Click Sonos, and unlink.
5. Go to the Sonos app and add Google Assistant as a voice assistant.

Hopefully everything works for you now.