ISO 8583 in depth: message types, data elements and the clearing message

ISO 8583 is the message standard for card transactions, and it is the language that the terminal, the acquirer, the scheme and the issuer use to talk to each other. Every card authorisation, every clearing file, and every reversal is an ISO 8583 message, and a payments professional who works in cards must be able to read one. The standard defines the message types, the data elements, and the format, and it has been in use since 1987, with the current version published in 2003. Although ISO 20022 is replacing ISO 8583 in some areas, the card schemes still use ISO 8583 for authorisation and clearing, and it will remain in production for many years. Why ISO 8583 matters is that it is the only way to understand what actually happened in a card transaction. The authorisation request, the authorisation response, the clearing message, and the reversal are all ISO 8583 messages, and each one carries the data elements that tell you the card number, the amount, the merchant, the response code, and the EMV data. If you cannot read an ISO 8583 message, you cannot investigate a failed transaction, you cannot reconcile a clearing file, and you cannot write a requirement for a card system. The standard is a technical subject, but it is also a business subject, because the data elements are the business facts of the transaction. The parties are the terminal, the acquirer, the scheme, and the issuer. The terminal creates the authorisation request, which is an 0100 message, and sends it to the acquirer. The acquirer forwards it to the scheme, which routes it to the issuer. The issuer returns an 0110 authorisation response, which travels back through the scheme and the acquirer to the terminal. At the end of the day, the acquirer sends a 0220 clearing message for each transaction, which is the financial advice that moves the money. If a transaction is reversed, the acquirer sends a 0420 reversal message. Each message type has a four-digit code called the MTI, the Message Type Indicator, and the first two digits tell you the version and the class, while the last two tell you the function. In practice the MTI table is the starting point. An 0100 is an authorisation request from the acquirer to the issuer. An 0110 is the authorisation response from the issuer. An 0200 is a financial transaction request, used for transactions that are authorised and cleared in one step. An 0220 is a financial transaction advice, used for clearing, where the acquirer tells the issuer that a transaction has happened and the money should move. An 0420 is a reversal advice, used when a transaction must be undone. An 0800 is a network management request, used for sign-on, sign-off, and echo tests. The MTI is always four digits, and the first digit is the version, which is 0 for ISO 8583:1987 and 2 for ISO 8583:2003, although most systems still use version 0. A worked example shows a clearing message. A customer buys GBP 45.20 at a supermarket. The authorisation request is an 0100 with data element 2, the primary account number, set to the card number; data element 3, the processing code, set to 000000 for a purchase; data element 4, the transaction amount, set to 000000004520; data element 41, the card acceptor terminal identification, set to the terminal ID; data element 42, the card acceptor identification code, set to the merchant ID; and data element 55, the EMV data, containing the ARQC and the transaction counter. The issuer returns an 0110 with data element 39, the response code, set to 00 for approval, and data element 38, the authorisation identification response, set to the approval code, for example 482913. At the end of the day, the acquirer sends an 0220 clearing message with the same data elements, plus data element 55, and the issuer books the transaction to the cardholder account. What happens when the message is wrong is a rejection or a misbooking. If a data element is missing or malformed, the scheme or the issuer will reject the message with a response code, typically 30 for a format error or 91 for an issuer unavailable. If the MTI is wrong, for example an 0100 sent where an 0220 was expected, the receiver will reject it. If the EMV data in field 55 is missing or incorrect, the issuer cannot verify the ARQC and will decline the transaction. The operations team must be able to read the message and identify the faulty data element, because the scheme will not tell you what is wrong, it will only tell you that the message was rejected. A common error is to send the amount in the wrong format, for example as a decimal instead of an integer number of minor units, which causes the issuer to authorise the wrong amount. The operational and accounting implications are that the operations team must monitor the message reject rate, the finance team must reconcile the clearing messages to the settlement, and the technology team must maintain the message specification. On the ledger, the 0100 authorisation creates a hold on the cardholder account, the 0220 clearing message creates the actual debit, and the 0420 reversal removes the hold and reverses the debit. The accounting team must be able to match each clearing message to its authorisation, because a clearing message without an authorisation is an exception that must be investigated. The reconciliation team must also check that the total of the clearing messages equals the settlement amount from the scheme. For a business analyst, ISO 8583 is a message specification subject. You must specify the MTI for each transaction type, the data elements required for each message, the format of each data element, the response codes, and the error handling. You must also specify the test cases: a valid authorisation, a valid clearing message, a reversal, a message with a missing data element, and a message with an invalid response code. A common gap is failing to specify data element 55, the EMV data, because it is a complex field with sub-elements, and a system that does not handle it correctly will fail EMV transactions. Takeaway: ISO 8583 is the language of card transactions, and the MTI tells you what the message is doing before you read a single data element. Further reading: ISO 8583:2003 for the message standard; the Visa Core Rules for the message flows; the Mastercard rules for clearing. Last reviewed 7 November 2026.