Driving a 2021 Audi A3 with carplay embedded I find that the situation is excatly the same as you guys. I´ve tried to figure out íf its with the OS (user) to allow some interaction with Webex and Carplay but so far I have not been able to find a root...

The user(s) you´re trying to add belong to a another organisation already? Pretty common error. Users can only be in one organisation at a time.

I believe that as long as your account ID matches on the new purchase you can do that. Myself eg. ran a 30 day trial and then converted to paid sub.