F34—PRIMARY ACCOUNT NUMBER, EXTENDED: This field is filled when the card number cannot be placed in F2 (card number) because it is longer than 19 digits or contains special characters. It is 28 characters long.
The difference between F2 and F34
Under normal conditions, the card number is carried in the F2 field of the ISO 8583 message. F2 is designed for card numbers of up to 19 digits consisting only of numbers. Since almost all debit and credit cards in use today have 16 digits, F2 is sufficient. F34 is a field reserved for carrying account numbers that do not fit this format.
When is it used?
F34 is used in special cases where numbers that do not fit the standard card number format need to be sent. For example, it is used in some systems when an account identifier with a different structure has to be carried instead of a card number. For this reason, F34 is used very rarely and does not appear in most card transaction messages.
It is a variable-length field
F34 is a field without a fixed length. A length indicator showing how many characters the content has is sent in front of the field, and the content can be at most the specified maximum length. In integrations, whether F34 is supported and when it will be used should be checked in the relevant network's message specification.
