Check the payment details. It will contain the message received by the gateway which will contain a hint as to why the payment failed.
Common reasons are as follows:
- There was an insufficient available balance on the credit card.
- The card has been deactivated.
- The card has been locked for fraud.
- The gateway service provider has detected duplicate transactions.
- The gateway could be misconfigured.
- AVS verification has failed
In most cases, your end customer will need to discuss this with their credit card issuer, or take additional steps to provide a working payment method in order to pay for the services you are providing them.