Promotional, coupon, and discount codes can cause quite a bit of friction when it comes to members earning points with in-app offers. Some of the brands on Drop offer automatic discounts; some examples include: store-wide sales where a promotional discount is applied at checkout, or automatic discounts for being a first-time customer. These promotions are permitted and your purchase will still qualify for Drop points.
However, if you manually applied a promotional code at checkout, (ie. a code that wasn't provided by Drop, or wasn't automatically applied by the brand) your purchase will not qualify to earn points.