I need help with a disposable mastercard.

So I bought a card from a store, but it wont work on the Nexon website. It's a 25$ Vanilla mastercard giftcard, and for some odd reason it won't work while I've had no problem with visa gift cards previously.

Am I doing it wrong?

Edit: Nvm, on the back in microscopic print it says I can't use it 24 hours after purchase.