Categories are the gift card brand names. E.G iTunes, Amazon.
Sub-categories are the types of gift cards we accept under a particular gift card brand.
For instance, if you want to trade $25 physical iTunes gift card. The category is “iTunes” and the sub-category will be “iTunes Physical Card ($25-$100)”.
It is just our way of arrangement in order not to get you confused. If you need further clarification, you can contact our customer support via live chat.