The Do Not Honor response code does not have a specific cause. Gateways have a limited number of responses and Do Not Honor is used for a number of different reasons. Some of the most common are:
- The credit card number or expiration date is invalid.
- There are insufficient funds in the cardholder’s account.
- The location or activity is suspicious.
- The bank’s fraud rules which can take many other factors into consideration.
Many times it is accompanied by other clues, but the only accurate way to know is to contact the issuing bank for clarification.