My Apple gift card is not letting me

So I’m trying to purchase something and it’s not letting me purchase anything I tried Apple support they try their best but it didn’t work not blaming Apple support about it. It’s a bug it’s been happening to people. They told me to log off of my Apple store page thingy. I did and they said to log back in and when I did, and I did try to purchase my thing and it didn’t let me. Can someone please help I purchased my gift card yesterday it wasn’t letting me I used this app before it. Let me do it but I don’t know what’s going on since I updated my iPhone it started it this never and this happened to me a couple of days ago