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# transactionIdentifier

A unique transaction identifier that the system generates.

```
var transactionIdentifier: String { get }
```

## Discussion

The system generates this value when you call [`setPostbacks(_:)`](/documentation/StoreKitTest/SKAdTestSession/setPostbacks(_:)). This value is an empty string otherwise.

Use this value to match the test postback with the response you receive from [`flushPostbacks(responses:)`](/documentation/StoreKitTest/SKAdTestSession/flushPostbacks(responses:)).

---

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