Whenever a payment is disputed, a dispute reason code is used by the issuer to let you and us know why the payment is charged back. You can see the reason code for the dispute in the Dispute page.
The reason code will give you an idea why the payment is disputed. Based on this, you can decide whether you would like to accept or defend the chargeback. For more details, read our list of Reason Codes and their respective description.
If you want to challenge the chargeback, the next step would be to consider the reason-code specific dispute defense requirements. For example, if you are defending a dispute because you have already refunded the cardholder, the refund details would be essential. The defense requirements are dependent on the reason code, aside from the general evidence used in responding to any dispute.
Please see this article on what defense documentation we recommend you to upload to increase the chance of winning.