Student paid for course but the system didn’t enroll him

Hi, a student paid through the site for a course, but he didn’t want to register and stayed as a guest (on the checkout page there is an option to stay as a guest).
So the payment was done, but he is not registered, and not enrolled in the course, an, of course, can’t take it.
So why in the first place the system allows paying as a guest without registration?