The Google Play Store may deem certain purchases out of the ordinary, for user security. This automatically prevents unwanted charges on your device.
In this case, the system has determined that your purchase was “high-risk”, canceling it in the process. This will clear itself automatically so don't worry; however, you will be unable to make purchases for 30 minutes or longer.
In the meantime, please verify that your name and billing address are exactly as listed on your credit card.
Unfortunately, we are unable to help you with this. If you continue receiving the “high-risk” alert, please contact Google for further assistance.