Originally Posted by
ursine1
There's only the one field on the website for entering a promo code, at the very beginning of the booking process. Southwest already disallows stacking by accepting only one code per reservation.
I wasn't clear enough. If you have a $20 off promo code or better yet a 20% off promo code and you use it to book flights during a conventionally conducted fare sale, you get the benefit of the sale plus the benefit of the promo. That is the "stacking" that Southwest wants to prevent.