Using prerequisites with an enrollment and ecommerce

Summary

The expected behavior of prerequisites (combined with ecommerce)

Content

We have several one-on-one sessions that I would like to attach a prerequisite to (a course) and before the User takes the course they would have to go out to PayPal to pay for it. I initially attached the prerequisite to the enrollment and that brought the User to PayPal and launched the course but when they completed the course it didn't enroll them in the session. If I attach the prerequisite to the session it will enroll them in the  session but won't take them out to PayPal . From what I have read the suggestion in this case