Why is my gift card getting declined when i try to put the information in the settings and when i have money in the card?

Every time i put in the info it says “Your payment method was declined” so when i put in my apple id it does nothing, i have tried numerous of times ive searched up everything possible and nothing works but i know the app “Wallet” doesn’t accept Vanilla gift cards. Heres the thing it used to work when i had a Vanilla gift card it used to go through and it let me buy whatever i wanted. now when i try to buy something on a app it also says “Your payment method is declined” so it asks me to change the security code and i do because its the same i put before and it doesnt do anything. Please help i cant let this card go to waste.