short answer is you cannot do this. In your case, to get the user to pay for the course once again, you would need to un-enrol them and reset their progress etc. You'd be better off creating a 2nd course (we use terms like “exam rewrite fee” and have the. purchase that one, then you could ‘release’ or allow the user to go through their 2nd attempt on the original course.

We use exam “windows’ so all users only have access to the exam during a specified time. This works well in our case but not sure if you can do the same. You might need use something else to ‘block’ the user from gaining access like a course status of “suspended”. Once the payment has been received, you can them change the status back to in progress.