I have set up my course to have to enrolment methods and both are visible, these are manual, and self-enrollment. I have set up the self enrolment to have a key. Created a new user, navigate to that course and I am asked to login and then I am straight in to the course. Without having to enter an enrolment key
I have noticed that if I set the "enable existing enrolments" to "yes" and press save it doesn't save, and it also strangely makes the self enrolment plugin hidden every time I save it.
I have the manual accounts plugin at the top with self-enrolment below