Typically, when a transaction is declined, it's because the billing address provided did not match the billing address of the payment method being used. Other common issues are zip codes, expiration dates and CCV/security codes. Please make sure that the payment information entered at check out matches the information associated with the payment method being used.
When a card is declined on our end, a pending charge might appear in the customer's online bank account. Don't worry, these charges usually do not go through, and the funds will be returned to the account at the banks discretion.
If you have any further questions, feel free to contact us here.