[Hall of Famer]

Well because the way this system is designed does not support advanced usage of public promocodes. And in fact to make a promocode available for each user only once, it will require a bit more coding than I had envisioned at the very beginning. You need to create a field in your database table prefix.promocodes to keep track of a list of users who have used this specific promocode. It may not be difficult, but sure can be tedious.