It would be easier for registrants if promo code appeared as a last step at the bottom. As it is, registrants have to scroll up and submit it again after all other info is entered - or they miss it.
The choice of where it sits on the page would be best, but the bottom would be vastly preferable to being stuck in the middle where it is now. I (obviously) have come up against this same issue and was pleased to see this comment and your response. Thank you!