Help please.
On Christmas last year my grandma gave me a $15 App Store & iTunes gift card. I immediately redeemed it correctly using the App Store and it added itself to my wallet app. I want to purchase a $4.99 app from the App Store using this gift card, however when I select the purchase method the gift card does not show up. My dads visa shows up on it, but not the gift card (dads visa because of family sharing). I have tried to use it to buy things from the App Store in the past but I always came to the same conclusion. I am now fed up. I have searched the internet multiple times and of course, as the internet goes, I came up with nothing. Can someone please tell me how to purchase apps with a $15 App Store & iTunes gift card that has been sitting in my wallet app untouched for almost a year?
iPhone 8, iOS 13