The Four Parties and the Card Transaction

The four party model is the foundation of every card payment. The four parties are the cardholder, the merchant, the issuer and the acquirer, and the card scheme sits above them as the rule maker and network operator. The cardholder is the customer who owns the card and makes the purchase. The merchant is the business that accepts the card. The issuer is the bank that gave the card to the customer and holds the card account. The acquirer is the bank or payment firm that provides card acceptance to the merchant and credits the merchant account. Once you can name these four parties for any transaction, you can trace the rest of the card lifecycle. Step one is the purchase, and the information flow runs from merchant to issuer. The customer presents the card at a terminal, on a website or in a wallet. The merchant terminal or gateway sends an authorisation request to its acquirer, with the card number, the amount, the merchant details, the date and the transaction type. The acquirer forwards the request to the card scheme, Visa or Mastercard, which routes it to the correct issuer using the first digits of the card number. At this point no money has moved. Only information has travelled, and the question being asked is simple: will the issuer approve this payment? Step two is the issuer decision, and the answer travels back along the same path. The issuer checks that the card is active, that the account has enough funds or credit, that the transaction does not breach a limit or a cardholder control, and that fraud scoring does not flag it. If the checks pass, the issuer approves, returns an approval code, and places a hold on the funds. The available balance falls, but the money has not left the account. If a check fails, the issuer declines and returns a response code, for example insufficient funds or suspected fraud. The approval or decline travels from issuer to scheme to acquirer to merchant, usually in one to two seconds, and the customer sees the result at the till or on screen. Step three is clearing, and it happens later, usually at the end of the day. The merchant batches its approved transactions and sends a clearing file to the acquirer. The acquirer sends the file to the scheme, which sorts the transactions, checks them, calculates interchange, and routes each transaction to the correct issuer. Clearing is where the authorised transaction becomes a financial obligation. The issuer posts the transaction to the cardholder account, and the acquirer prepares to pay the merchant. An authorisation that is never cleared never becomes a charge, which is why a reversed authorisation simply releases the hold. Step four is settlement, and it is the movement of money. The scheme calculates a net settlement position for each issuer and each acquirer from the clearing files. Each participant settles one net amount with the scheme, instead of settling separately with every other bank. Issuers that owe more than they are owed pay the scheme, and acquirers that are owed more receive from the scheme. The acquirer then credits the merchant, usually one to two business days after the purchase, minus the merchant service charge. For a credit card the cardholder repays the issuer later under the card terms, and for a debit card the account was already debited at posting. Fees flow in the opposite direction to the purchase, and the analyst must be able to explain them. The merchant pays a merchant service charge to the acquirer. From that charge the acquirer pays interchange to the issuer, pays scheme fees to the scheme, and keeps the remainder as its margin. Interchange is the largest part, and it varies by card type, by channel and by market. Exceptions can interrupt the flow at every step, and they are part of the model. A decline at authorisation stops the purchase before clearing. A timeout, where no response arrives, leaves the status unknown, so the merchant must reverse the authorisation or check the status before retrying. A duplicate authorisation can place two holds on the same purchase. A chargeback after settlement reverses the flow, moving money back from acquirer to issuer and then to the cardholder, with fees and evidence attached. A good analyst designs for these paths from the start, not as afterthoughts.