When a card is declined.
How do you fix it when your card is declined for fraudulent activity and it wasn’t fraudulent?
iPhone 7, iOS 12
Either use a different card, or, and if iTunes have blocked it, see if they will unblock it : http://www.apple.com/support/itunes/ww (click on your country's flag, the country where you live, and which is therefore the country on the account ; click on Contact Support towards the top right ; click on Get Help under 'Talk To Us’)