Couldn’t use Apple account balance at Apple store

I loaded a $25 Apple gift card to my account. It shows my apple account balance has $20.72 (I used some of it on the App Store). I tried to use the remaining balance at an Apple Store, but I couldn’t find a QR code or other code to redeem. I also don’t have an ITunes pass in my wallet, and The instructions to add one don’t work (couldn’t find an option to add iTunes pass). what can I do?