NAB EFTPOS error 51
An 05 decline code is a general Do Not Honor declined response. This is the most common and general declined message for transactions that are blocked by the bank that issued the card.
Generally, the response code returned from our system is the actual response returned directly from the customer's credit card issuing bank. If it is determined that the customer's issuing bank is declining the transaction, there is nothing PayJunction can do to override the decline response.
We recommend asking the customer to call the number on the back of the card to speak with the bank. The customer can explain that they are trying to issue a payment and they should ask the bank to allow the transaction. Otherwise, the customer will need to provide an alternate method of payment.