What is a merchant ID (MID)?
A merchant ID (MID) is the unique number an acquirer assigns to a merchant account. It identifies the merchant in every card transaction and tells the acquirer where to settle funds, which fees to apply and where to send disputes. A MID is specific to one acquirer, so a merchant with several acquirers has several MIDs.
In detail
A merchant ID is the account number of a merchant in an acquirer’s system. It is created when the merchant is approved and stays attached to every transaction.
What a MID carries
- Identity: the legal entity and the trading name.
- Category: one merchant category code (MCC).
- Settlement: the bank account and currency where funds are paid.
- Pricing: the fees agreed with the acquirer.
- Risk: limits, reserves and monitoring ratios.
How it is used
In the message standard for card payments, the MID travels in the card acceptor identification code, a field of up to 15 characters. The acquirer uses it to group transactions for clearing and settlement. Disputes, statements and scheme monitoring programs are also organized per MID.
A MID is not global. Each acquirer issues its own, in its own format. Payment facilitators add another layer: sub-merchants are identified by a sub-merchant ID under the facilitator’s structure.
See MID and TID for how the identifiers fit together, and PayFac vs ISO for the two models. Operators attach acquirer accounts to merchants during payment stack activation.