Hi,
To put it in simple terms, the purchase was made without a knowledge or approval of the cardholder. As a result, the payment is being reversed by the cardholder's bank.
You will find a more detailed explanation on the following thread: https://www.cgtrader.com/forum/general-discussions/how-to-prevent-the-buyer-using-the-stolen-credit-account
Best of luck,
Mantas
CGT Support