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# adImpressionIdentifier

A random value to use for added security.

```
var adImpressionIdentifier: String { get set }
```

## Discussion

Ad networks set the value of this property to a random value (nonce) at the time of the ad impression.

> Important:
> When you generate ``doc://com.apple.storekit/documentation/StoreKit/SKAdImpression/signature``, which is the signature value, you must sign the ``doc://com.apple.storekit/documentation/StoreKit/SKAdImpression/adImpressionIdentifier`` as an all-lowercase UUID string representation.

---

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