Hi , sorry for this delay. Somehow we have missed your mail.
Regarding this issue “But I’m now finding that when testing and I submit a purchase, I don’t get redirected to the course page when purchase is complete. After clicking the final button to complete a purchase, the page loads for a very long time then get redirected to the Moodle homepage”, is this a general flow you are getting or this issue is only with coupon?
Also, will it be possible for your to share a admin access so we can debug this on your end.