It happens when the credit card information you entered, typically the post/zip code etc, does not match the file with the card-issuing bank, and then you tried again and checked out successfully with corrected information.
In this situation, the first failed payment was blocked by our system for security reason. However, this charge may temporarily appear as pending on your statement before being removed. Normally, the payment would be bounced back to your account automatically within a few hours. You can also contact your bank for any further assistance.