We can. I never said I didn’t have any solution to this use-case. I was trying to use the same pattern we established for OrderForms (hence the whole pre-fill commonality)
Every promotion is different. As I said earlier, in some cases, we want this to be an exclusive offer to the list that we are targeting. In a dream scenario, each individual would get a personal code, but since InfusionSoft does not support individualized PromoCodes, this is overly burdensome. One way to simulate this single-use PromoCode feature, would be keep the actual PromoCode value private, by having the (custom) Landing Page, pass along the PromoCode and pre-fill it for the customer. It is not totally secure, but it slightly obscures the code and prevents unwanted sharing.
Even in your situation with the custom Thank-You, I’d ask the same question, how can we streamline the checkout UX? If there is a link for “add to cart” on the custom thank you page for the product, I’d still want to pre-fill with as much data as possible, since I’ve already collected, name, email address (and I know the promo code.) In order to streamline the check-out I’d be looking to pre-fill off the action on the Thank-You page, so the Customer does not need to enter data multiple times.
The heart of the question, is what is the fewest numbers of actions we require of our users to get the desired outcome? I know of multiple work arounds, and its not that I don’t know another way to solve this, I"m looking for an optimal way to solve this that integrates with out (custom) forms. Ideally with as similar a pattern as possible.