No, when a person is enrolled into a course, he/she will not be asked for payment. See enrolment as an OR situation: once you are enrolled, no other enrolment checks are done. The reason is simple: when you payed for a course by PayPal, you will not be asked again to pay your course by Stripe.
So the same is valid here, once you are enrolled by course completion, you will not be asked for payment.