We offer various discounts on our main products for different reasons to different clients. It would be extreamly helpful to be able to create a coupon code to provide to customers to apply to a single payment link - rather than having to create separate links for each person with a discount. Then, we could send our prospects to a sales page with a link to the full price, and they enter a coupon/scholarship code (if they have been assigned one) and it automatcially applies to the price and checks them out at the discounted price.
@AAPorter have you submitted this to the Ideas forum? Or maybe looked to see if someone else has and you can upvote & comment with your use case? I doubt you’re the only user to be thinking of payments and discounts this way. HubSpot pays attention to those Ideas. 
Everyone who finds this post, this idea was submitted. Please upvote it here: https://community.hubspot.com/t5/HubSpot-Ideas/Feature-Request-Coupon-Codes/idc-p/696937#M123738
Done. thanks @SStewart3
UPDATE: This feature has now been added!! Create and use discount codes
Thank you for sharing, @SStewart3!