I registered a domain (for ex. mydomain.com) and I opened a Cloud Identity (free edition) account attached to that domain.
Then I configured a Google Cloud access for this Admin user. So, I finally had my Cloud Identity account with my user as an admin, my organization and my Google Cloud account with which I can access Google Cloud Console.
After accessing Google Cloud Console, I setted up the payment and billing profile for my organization; I created also some groups and additional users through Google Admin console. All of them belong to mydomain.com; so for example I created an additional user [email protected] that belong to gcp-network-admins and gcp-security-admins groups.
[email protected] received an invitation email. If he tries to login to Google Cloud Console he gets a 3 step wizard where on the last step the system ask him to enter billing and payment info to access and start using Google Cloud. I don't understand why and I'm not sure if I did something wrong.
kind regards, Matt
Posting as an answer.
Based on my experience, Upon my first login I tried to link my GCP console to Organization Billing account. Worth to check also if the user was created is also a biling user or owner.