This sometimes happens when the credit card information you entered the first time, typically the post/zip code, etc does not match the card-issuing bank's file. On your second attempt, you checked out successfully using the correct information.
In this situation, the first failed payment was blocked by our system for security reasons. However, this charge may temporarily appear as pending on your statement before being removed. Usually, the refund will return to your account within a few hours. You can also contact your bank for any further assistance.