if you buy 'upgrade stash tab to premium', it doesn't give you mystery box

under announcements, it says "Until the end of the sale, we’re offering one free Dawn of the Hunt Mystery Box when you spend any amount of points in the store. This means you can purchase anything discounted in the sale or any other microtransaction from the store and receive one Dawn of the Hunt Mystery Box as a gift from us. This offer is available on both PC and Consoles."

i bought an upgrade for 10 coins that upgrades one of my stash tabs to premium so that i can sell. however, it does not give you a mystery box. it's a part of the sale and that should give a mystery box.