I have opened

I have opened support access for 5 days. theukonline.net Site has CoursePressPro and has two courses up there. Have tried our Paypal and all is working well. How do I link payment finished back to their chosen Course so students can do the Course please? I have the pages up that come back after payment, just dont know how to link it back to the Course, I wondered if there was a shortcode I have missed, or a step I haven't completed.
Thank you