Why my debit card unavailable to purchase apps

Debit cards are not longer accepted in many locations. You will have to use

a credit card or an iTunes gift card.

In countries where the iTunes Store only sells apps, the accepted payment

methods are Visa, MasterCard, and American Express. Other payment types s

uch as gift cards, store credit, monthly allowances, ClickandBuy, and PayPal

are not accepted. Depending on your App Store country, prices may be listed in

your local currency, US Dollars, or Euros. http://support.apple.com/kb/HT5552

You need to contact apple.

This is a user to user forum, we can not help you with credit card issues.

https://www.apple.com/support/itunes/contact/

you need to activate international use on your debit card Then it will work .