Authorize.Net · Transaction Response Reason Code

Authorize.Net Transaction Response Reason Code 6: Invalid Card Number

The credit card number is invalid. Ask the customer to verify and re-enter the card number.

What it means

Authorize.Net Response Reason Code 6 indicates that the primary account number (PAN) submitted fails basic gateway-level validity checks, such as the Luhn algorithm or supported card scheme formats. Because the card number is fundamentally malformed, the gateway blocks the transaction and returns a transId of 0, meaning it never reaches the processor or the issuing bank for authorization.

Classification & retryability

hardtechnicalRetryable: no

Common causes

The customer made a typographical error while entering their credit card number during checkout.
The submitted card number fails the Luhn validation check at the gateway level.
The card number structure does not match any of the card schemes supported by the merchant's Authorize.Net account.
In sandbox environments, an invalid test card number was used, or the API is improperly configured for test mode.

How to resolve it

Because the transaction never reaches the issuing bank, this error must be corrected at the point of entry. The submitted card data must be discarded, and the customer must be prompted to re-enter their card details. Ensure that your checkout form includes basic front-end validation (like Luhn checks and card brand detection) to catch these errors before they are sent to the Authorize.Net API.

For merchants

Do not attempt to automatically retry this transaction with the same payment data, as the gateway will continue to block it. Instead, configure your payment workflow to immediately prompt the customer for a correction. Review your sandbox testing procedures if this occurs frequently in development, ensuring you are using valid Authorize.Net test card numbers.

For customers

Carefully review the credit card number you entered for typos and try submitting the payment again. If you continue to experience issues, verify that you are using a card brand accepted by the merchant, or try an alternative payment method.