Create onboarding member orgnanization and its organization via our application

Hi all,
We would like to allow users to login our app and create their own organization.
The meaning of that is that new user has to create his first organization and also should be a memeber of this organization (as admin role).
The problem is that he can’t create an organization because he didn’t signup. And he can’t signup if he didn’t creat an orgnazition first.

The solution can be by defining “Types of Users” in our app as “both”.
But than the user has the ability to signup without be apart of any organization. And this senario we don’t want to be allowed

I will be happy to know what is the right flow to solve this issue.