Track F · Foundations

You will be able to

• Decode an MTI, POS entry mode, POS condition code, response code, MCC and currency code
• Know which response codes mean retry and which mean do not retry

The lesson

1. Why it matters
2. The concept
3. In the real world
4. Common mistakes
5. What to test

In the module

• The lesson, with diagrams, common mistakes and what to test
• A worked example you can change: Decoding a message's codes
• Practice: 3 kinds of generated exercise, each with a step-by-step solution
• A quiz of 8 questions

Key terms

Action code

The three-digit result code of ISO 8583:1993 and later (field 39 there), which replaces the two-digit response code of the 1987 version.

Approval code (Authorisation code)

Field 38: the six-character code the issuer returns with an approval. It is printed on the receipt and needed for completions and some refunds.

Country code

ISO 3166 three-digit numeric code of a country, used for the acquiring institution (field 19) and, in EMV, for the terminal (tag 9F1A).

Currency code

ISO 4217 three-digit code of the amount's currency (field 49): 840 USD, 124 CAD, 978 EUR. The code also gives the number of decimal places.

MCC (Merchant category code)

Four digits that classify the merchant's business (field 18). Networks use it for interchange, limits and risk rules.

Merchant ID (MID, card acceptor ID)

Field 42: fifteen characters identifying the merchant at the acquirer.

Minor unit (Currency exponent)

The number of decimals of a currency. Amounts in messages are integers in the minor unit: 000000001050 is 10.50 USD but 1050 JPY.

POS condition code

Field 25 in ISO 8583:1987: the conditions at the point of sale, such as cardholder present, mail order or unattended terminal.

POS entry mode

Field 22: how the PAN was read (manual, stripe, chip, contactless, fallback) and whether the terminal can take a PIN.

Processing code

Field 3, six digits: the transaction type (00 purchase, 01 cash, 09 purchase with cashback, 20 refund, 31 balance inquiry), then the from-account and to-account types.

Response code

Field 39 of the response: 00 approved, 05 do not honour, 51 insufficient funds, 55 incorrect PIN, 91 issuer unavailable and so on. Values beyond the common ones are network-specific.

RRN (Retrieval reference number)

Field 37: a twelve-character reference that stays with the transaction through clearing and disputes.

STAN (System trace audit number)

Field 11: a six-digit number the sender gives each message. With the terminal and date it matches responses and reversals to requests.

Terminal ID (TID)

Field 41: eight characters identifying the terminal at the acquirer.

Tools for this module: Payment CodesCurrency Codes

Read the opening of the lesson →