[Glossary](https://blnkfinance.com/glossary) Reference # What is a transaction reference? Reference A reference is the unique key you put on a transaction so the ledger can refuse a duplicate. If you send the same reference twice, the second request does not create a second movement. People often call this idempotency. The field name is reference. ## How does a reference work? You generate a key in your app, one per intended movement. The ledger stores it. A retry with the same key returns the original transaction. A new movement needs a new key. That is the whole contract. Timeouts, double clicks, and webhook retries all resend work. Without a reference you post twice. With one, the ledger treats the retry as the same transfer. ## Reference vs transaction id The ledger assigns the transaction id. You assign the reference. Look up by reference when your app needs to know what happened to a submit it already made. Look up by id when you already have the ledger’s record. ## What makes a good reference? Stable, unique, and generated before you call the API. Do not derive it from the amount alone. Do not reuse it for a refund or a retry that is meant to be a new movement. A UUID or an idempotency key from your job runner is enough. In Blnk, reference is required on every transaction. It is how the ledger implements idempotency. After a queued transfer is processed, lookups that need the next state use the parent chain. See [transactions](https://docs.blnkfinance.com/transactions/introduction) and the [idempotency guide](https://blnkfinance.com/blog/how-to-handle-idempotency-in-your-financial-app-using-the-blnk-ledger). Related terms - [Idempotency](https://blnkfinance.com/glossary/idempotency) - [Transaction](https://blnkfinance.com/glossary/transaction) - [Webhook](https://blnkfinance.com/glossary/webhook) - [Parent transaction](https://blnkfinance.com/glossary/parent-transaction)