Who has access to which course.
Four states, and only one grants access
Active means the student can see the course. Awaiting payment means not yet. Cancelled and expired do not grant access either.
"I paid but I cannot see the course" almost always means the enrolment is still awaiting payment.
Enrolling by hand is allowed
Nobody has to buy anything. You can create an enrolment directly — for a guest student, as compensation, or when migrating from an earlier system.
An enrolment can expire
Access can be permanent or run until a date. When that date passes the state becomes expired and access closes, with nobody doing anything.
Progress stays with the enrolment
If an enrolment is cancelled and later reactivated, what the student had already completed is not lost. Progress belongs to the enrolment, not to its current state.