I want to add a user from another AAD tenant but that fails with the message 'no user exists with this user name in a directory to which you have access'.
The setup: I have two Office 365 subscriptions and associated Azure subscriptions and AAD tenants, lets call them sub-A and sub-B.
On sub-A I have a user 'user@domain.com' (MSA) that is Global Admin in Azure AD tenant A. On sub-B I have that same user also as Global Admin in Azure AD tenant B.
When I sign in (in two different browsers) to both Azure subscriptions with the same MSA user@domain.com, I am unable to add a user from tenant B to tenant A or vice versa. I always get the error 'no user exists with this user name in a directory to which you have access'.
Am I misunderstanding the documentation that specifies I can add users from other tenants to an Azure AD tenant?