Nowhere in the text does it state that a coupon isnt usable when buying items for GP, yet there is no option for doing so.
Furthermore the text in itself is contradictory by saying it is valid for "All" items then in the next sentence it suddenly isnt valid for discounted or event items.
"This coupon is valid for 50% off All items. Not valid for discounted or event items. All purchases w/ coupons are final. Cannot be used for gifting."

Picture: https://i.gyazo.com/2e2225084a601f2b...8629530001.jpg