Card Sequence Number

A card sequence number, more formally the PAN sequence number, is a two-digit value written into an EMV chip that identifies one particular physical card among several that share the same primary account number. Issuers use it when they give the same card number to more than one card, for example when issuing a card to an additional cardholder on the account or replacing a damaged card without changing the number. The value is read from the chip during an EMV transaction, sent to the issuer with the authorisation request, and used together with the card number to select the right cryptographic keys and verify the chip's cryptogram. If the number is missing or wrong, the issuer may be unable to validate the card and decline the payment. It is not printed on the card and is separate from the card's security code and expiry date. Card-not-present payments do not use it, since no chip is read.