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# lineItemId

A unique identifier for the line item, that you determine.

```
string lineItemId
```

## Discussion

Maximum length: 128

The [`lineItemId`](/documentation/ExternalPurchaseServerAPI/lineItemId) string must be unique for each app. Using UUIDs is recommended.
All line item objects have a [`lineItemId`](/documentation/ExternalPurchaseServerAPI/lineItemId), including:

- [`OneTimeBuyLineItem`](/documentation/ExternalPurchaseServerAPI/OneTimeBuyLineItem)
- [`RefundLineItem`](/documentation/ExternalPurchaseServerAPI/RefundLineItem)
- [`SubscriptionBuyLineItem`](/documentation/ExternalPurchaseServerAPI/SubscriptionBuyLineItem)

---

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