No such thing as an Apple Pay account.
Apple Pay uses your own credit cards or debit cards, including Apple Card. There is no account in and of itself for Apple Pay.
Apple Gift Cards cannot be redeemed onto the Apple Cash account if that is what you mean. Apple Cash holds actual money from the Apple (credit card) Card cash back or transferred from a linked bank account. Apple Gift cards can only be redeemed onto your Apple ID account.
From there you can buy Apps, games, music, movies and even physical hardware products through the Apple Store App.
Link-> What you can buy with your Apple Gift Card or Apple Account balance - Apple Support