HeptaPay use PayPal for secure checkout. We do not store your card/bank details. When you face an issue checking out, check the following:
Make sure you have selected the correct country. The country should be the country from where your card was issued and not the country of residence or the country your are paying a bill for.
Make sure you have the entered the correct address (Postal or Zip code) as reflected in your bank. Some banks do not ask for these details when applying for a card. If this is the case, visit your bank to update address details.
You account is funced.