What is the difference between a MID and a TID?
A MID identifies the merchant account, and a TID identifies a specific terminal or point of acceptance under that account. The MID tells the acquirer who must be paid. The TID tells which device, till or online checkout took the payment. One MID usually has several TIDs, and both are sent in every card transaction.
In detail
The two identifiers work at different levels. The MID is the account, and the TID is the device or channel.
MID
- Answers: who is paid?
- Assigned by: the acquirer.
- Format: up to 15 characters in ISO 8583.
- Used for: settlement, pricing, disputes, monitoring.
TID
- Answers: where was the payment taken?
- Assigned by: the acquirer or processor.
- Format: 8 characters in ISO 8583.
- Used for: terminal management, batch closing, store and till reporting.
A shop with five terminals typically has one MID and five TIDs. An online store has a TID too, even with no physical device, because the gateway connection needs one.
When a payout looks wrong, the MID shows which account was credited and the TIDs show which devices contributed. When a terminal is replaced, the TID may be kept or changed, and the inventory must be updated either way.
See MID and TID for the full picture and settlement and payout for how funds follow the MID. For stores, the in-store payments Matcher page explains how terminal transactions are matched to orders.