Unable to download any apps

I just got an IPhone 8,

And I put in all my banking details (visa debit card) and I was able to download apps and stuff. I haven’t made any purchases at all except 1. But I tried downloading an app today (duolingo) but for some reason it keeps saying my payment method is invalid and is declined??

I don’t understand. I haven’t bought anything except for 1 song from iTunes which was a while ago.