How a card acceptor ID works
Card messages have a dedicated field for the code. Mastercard's Transaction Processing Rules of 9 June 2026 refer to it as data element 42, the acceptor ID code, which holds the merchant ID.
The acquirer issues the code when the merchant account is opened, and the terminal or gateway puts it in each request. Together with the terminal ID, the code tells the acquirer, the scheme and the issuer where a payment was taken.
The Visa Core Rules of 18 April 2026 list the acquirer-assigned merchant ID and the card acceptor identification as two separate items in the merchant data that an acquirer provides to Visa.
Who meets a card acceptor ID
A gateway stores one for each merchant account at each acquirer. One merchant can have several: per currency, per outlet, per sales channel or per acquirer.
The code appears in settlement reports, dispute files and on receipts. A payment sent under the wrong one settles to the wrong account, which makes the mapping a part of onboarding that is checked before the first live payment.
Card acceptor ID, merchant ID or terminal ID?
- Merchant ID
- The acquirer's account number for the merchant. Often identical to the card acceptor ID, and used as its everyday name.
- Terminal ID
- Identifies one device, or one virtual terminal, under a merchant.
- Merchant category code
- Says what kind of business the merchant is, not which merchant.
Where a card acceptor ID shows up in a platform
Modules that do the work
- Card acquiringCard acceptance on the phone, in store and online, through the acquirer you choose.
- Merchant onboardingBusiness sign-up, verification and underwriting, from application to first payment.
- BackofficeOne console to run the platform: customers, money, risk, content and staff permissions.
Platforms that need it
Where it is written
The laws and standards this page's facts come from.
- Mastercard Transaction Processing Rules, 9 June 2026: DE 42, Acceptor ID Code (Mastercard)
- Visa Core Rules and Visa Product and Service Rules, 18 April 2026: 5.1.1.1 (Visa)
General information, not legal advice: what applies to you depends on your services and your market.