I — like apparently so many others — have tried a million times to get Google Assistant connected to my Beam. It worked some years ago, but I must have made some changes...
Anyway, I now got it to work by unlinking the Sonos account (which must have been created years ago) on Google. You want to go to your matching Google account and under ‘Security’ click on ‘Linked Accounts’. There, if you have an old Sonos account, unlink that. And then go back to Google Home (or the Sonos app, I guess) and do the normal procedure for adding a device. (this is the direct link to ‘Linked Accounts’: https://myaccount.google.com/accountlinking)