Hi ​@Foobar 

Welcome to the Sonos Community!

Sorry to hear of this issue you are having with adding Google Assistant to your Sonos speaker(s).

There was a brief outage, which has now been resolved. Please try again.

If you still see an error, please reboot your phone, speaker and router - reboot the router by switching it off for at least 30 seconds.

if you still see the same error afterwards, I recommend you get in touch with our technical support team who have tools at their disposal that will allow them to give you advice specific to your Sonos system and what it reports.

I hope this helps.