Based on your country of residence and country you have selected under your Apple ID --> Payment methods that you can use with your Apple ID - Apple ...
Have you a Debit/Credit card issued to you that is valid internationally and from the same Country / Region as your Apple ID?
Know it here --> If your payment method is declined in the App Store or iTunes ...
Check the following
- The payment method that you are adding is of the same country as that of App Store Country on your iPhone
- You have a valid payment plan debit/credit card from an authorized bank from the same country
- Payment methods that you can use with your Apple ID - Apple Support
- Learn more about family purchases and payments.
- Please check if your Debit/Credit card is valid internationally
If you can't download, make purchases, or update apps, including free apps, you must update your payment method or add a new one. If you verified that a payment method is available in your country or region and you're still having trouble, learn more.