There is a bug EITHER in the Delete User endpoint OR the documentation of the User Management API.  The documentation states that expects the userId as a path parameter. It’s definition of userId is: Unique identifier or exact email address of the user. In the Delete User endpoint, providing the exact email address returns 404 / not found, but providing the userId as returned by the Get User endpoint works fine.

In the Get User endpoint, the documentation for the path parameter of userId is the same and it works fine for email address

While it could be that the documentation is incorrect, I think the Get User and Delete User should be consistent from the perspective of good API design

Here is the link to the Delete User documentation as reference: Delete a user in tenant | Nintex Automation Cloud