My payment is showing payment declined

See this Apple article: If your payment method is declined in the App Store or iTunes Store

https://support.apple.com/en-us/HT203005

A “payment declined” or “card declined" message means that the issuer of the credit or debit card you have on file in your iTunes account rejected a charge or account confirmation. It is not an Apple problem; Apple is just passing through the message from your issuer. There are a number of reasons the charge or verification might be declined:

• Insufficient balance or account in arrears
• Account suspended for suspected fraud (not necessarily by you)
• Error in card number
• Wrong expiration date
• Wrong security (CVV) code
• Address in your iTunes account does not match exactly the billing address for the card
• The card was not issued in the country of the iTunes store
• The card type is not supported in your country
• You are connected through a VPN provider that does not terminate in the country of the iTunes store you are connected to.

See also the article link in Raicya’s post.