Not getting organizations list under a user

I am getting an empty response for the following API:
https://api.github.com/users/{username}/orgs
Is there any other way that I can get the list of organizations under a given user

There is no concept of organizations under a user.
Only repositories under a user or organization.

A user can be a member/have some permission on an organization.

GET /user/orgs would return the list of orgs the currently authenticated user has some permissions on.
You cannot enquire what permissions another user has on organizations for obvious security reasons