Auth0 UserRegistration/CreateUser Using Management Api .net

Hello In my project I have implemented Auth0 Login. Now the problem is Anyone can just login. When a person visit my spa login page . He can just click Login create a auth0 account and login. I ant to prevent this. I want to create/register some users from my backend ASP.Net Core Web api. I belive i can achive this using Auth0 Management api OR Auth0.Management Nuggent package. The Auth0 documentation are really confusing. Can Some one explain the steps to me, This is the flow i want
User Fill in Registration form and send it to my Anonymous End of API
API usess these details and Create a user in Auth0
Now this user can loginto my application
The login paart is complete how do i register a user?