Callback used by store implementations to interact with Unity IAP.
| products | Gets the item with local identifier. |
| OnProductsRetrieved | Complete setup by providing a list of available products, complete with metadata and any associated purchase receipts and transaction IDs. |
| OnPurchaseFailed | Call to indicate to Unity IAP that a purchase failed. |
| OnPurchaseSucceeded | Inform Unity IAP of a purchase. |
| OnSetupFailed | Indicate that IAP is unavailable for a specific reason, such as IAP being disabled in device settings. |