Multisite Subsite user registration not redirected to main domain


I use multisite and my main site is

I set up an e-course on

I will need people to be able to register directly on this site using:

At this point, it redirects to the user registration which is complicated for both me, and the user.

I researched how I can fix this problem, to no avail. The closest thing I found that might help is this:

Unfortunately, that advice is terribly way over my technical capability and confidence. There must be a more simple solution to having people register directly for the class on the subsite instead of redirecting to the main site?

Advice is greatly appreciated.