Newly added Team members are not authorized

Hi,

I invited a new member to my team (I'm the owner of the team).

The member gets an invitation, but after login through the link in the E-Mail,  the new team member is told "You don't have access to the organization" Please contact the administrator.

I followed the same steps in the past with other members and until recently it worked fine. But now it is not working anymore. Where can I set the permission to access the team for the new member?

(I'm using teams without office 365)

Thanks,

Martin