Apple Pay /Gift Card

So I got an Apple Gift card, which I thought I added to my Apple Pay? My Apple Pay shows a $0 balance. So I downloaded the Apple store just to make sure I still have my gift card balance, it shows I still have $25.... so how can I use it? This Apple gift card never shows up for me to use when I’m trying to purchase anything in the Apple store, or when I’m playing games on my phone? What can I do with this now that it’s in my phone and I can’t find the physical card?? Can someone please help me??? - from a dumb founded mama who doesn’t want to look like an idiot asking her daddy what to do! 😬🥴😝 Thanks in advance