Limit Discount Codes per Checkout

It would be helpful to have an optional setting that limits customers to one discount code per checkout.

This would be particularly useful for affiliate and referral programs, where each customer should use only one creator’s code. Allowing multiple codes may lead to unintended discount combinations and make affiliate attribution and commission tracking more difficult.

Ideally, customers could remove the first code before applying a different one, but would not be able to use multiple codes on the same purchase.