What is a transaction ID?

In short

A transaction ID is the unique reference that a payment system gives to one payment, so that the payment can be found, tracked and matched in records afterwards. A single payment usually carries several transaction IDs, because each party that handles the payment assigns a reference of its own.

Also called
Transaction reference, Payment ID, Payment reference, Txn ID
Family
Accepting payments
Facts checked

The IDs one card payment carries

  • The merchant's order or invoice number
  • The gateway's or PSP's payment ID, returned by its API
  • The retrieval reference number, from the acquiring side
  • The scheme transaction ID, from the card network
  • The acquirer reference number, on the cleared transaction
  • The authorisation code, from the issuer

On a blockchain the equivalent is the transaction hash, and on a bank transfer the end-to-end reference.

How a transaction ID is used

Customer support searches by it, webhooks and API calls quote it, and refunds and captures point to the ID of the payment they act on. Reconciliation is the work of matching the same payment across IDs: the PSP's settlement report against the merchant's orders and the bank statement.

What a payment system needs from its transaction IDs

An internal ID that is unique, never reused and assigned before any outside party is called, so that a payment that times out can still be found. The system stores every external reference against that ID and makes each one searchable. An idempotency key, sent by the caller, is a separate thing: it stops a repeated request from creating a second payment.

Where a transaction ID shows up in a platform

Modules that do the work

Platforms that need it

Every term

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