Appstore bug

Hello I have reached out because of a bug on my phone. I try to download any free app and it says “payment method declined” I change the card to the correct information like it asks and it doesn’t work still. I’ve even searched up youtube tutorials and nothing has helped. I don’t get what is going on. my phone is up to date and I have money on my cashapp card which is linked to my phone. It is the only method linked to my phone. does anyone know how to fix this?