For anything to act as money, it must be accepted as a medium of exchange by all and should act as a measure and store of value. This gift card is accepted only at selected stores and cannot act as a measure and store of value. It can only buy certain products.
Suppose the card is worth $100, but you need to buy something worth $75, and you do not want anything else for $15, you cannot use the card as you need to redeem it in full for $100. On the other hand, the card has a fixed value, and it is applicable for a certain period only; thus, it cannot act as a store of value.
Moreover,it must be a legal tender for anything to act as money. That is, the government must recognize it as money. Since gift cards are not legal tender thus, they cannot act as money.