cannot install google assistant on sonos app

hello.

I cannot add google assistant on my sonos app.

See below what I have tried:

1. i can see all my 4 sonos linked to my Google home app in their respective rooms
2. I have unliked them and then linked them back again 
3. I have rebooted all 4 sonos speakers
4. both my google assistant / home and sonos app are up to date
5. they are on the same wifi network
6. I am logged in one google account
7. Spotify is my default music service on both google home and it is linked in the sonos app with my unique login details
8. I still cannot add google assistant to my sonos app.

Can you please help.

Thanks