Unable to purchase iCloud storage for iPhone using debit card

If your debit card is not working, you will have to try another card or payment method.

If you need to change or update your Apple Account payment method - Apple Support

Payment methods that you can use with your Apple Account - Apple Support

chimdiebube wrote:

My country is not listed in the link

What country is your Apple account registered to?

Possibly. Check your country in the second link I provided. It lists payment methods Apple will accept.