If you're trying to pay via the Apple AppStore or the Google Play Store, please contact their service directly. Make sure you have sufficient funds for the payment method and that:
• Your card is registered in the same country as your account
• Your card has not expired or is blocked
• Your card is activated for purchases abroad as well as online and regular transactions. Look for these options on your bank's mobile app
• Your bank or payment provider has the correct information
After these steps, if you still can’t pay, please contact the support of the Store you want to purchase through.