Question: appstore cannot process payment
I'm trying to download an app in my IPhone 7 (which is up-to-date with the iOS). First the Appstore asks me to sign in with Apple ID, I sign in and when is downloading it sends me to verify my payment: "verification required". I go to verify my payment method and introduce the required information and clicked on the DONE button but I keep on receiving the same message over and over again: "The iTunes Store is unable to process purchases at this time. Please try again later". Even, I tried to verify and introduce the billing info from the "settings" but the same outcome.
Is it something related to the system or this is something related to my account itself? What can I do to fix this problem as I want to download a couple of Apps for my personal training and is not possible since one month now. I bought the iPhone end of last year and I hadn't try to download anything since then.
iPhone 7, iOS 11.2.6