When your store’s RetrieveProducts method is called it should fetch the latest product metadata and, optionally, ownership status for the current user.
When this process completes your store should call the OnProductsRetrieved method of the IStoreCallback supplied to your store upon initialisation, supplying a collection of ProductDescription that represent the items available for purchase.
Where products are owned by the user, your store may fill in the receipt and transaction ID fields of ProductDescription; Unity IAPSee IAP More info
See in Glossary will invoke the application’s ProcessPurchase method for any transactions the application has not already processed.
Note that if the user is offline your store should retry until the user regains connectivity, taking care to avoid impacting game performance through aggressive polling.
If products cannot be retrieved due to an unrecoverable error, such as the developer making an error with their store configuration, you should call the OnSetupFailed method of the IStoreCallback, indicating the InitializationFailureReason responsible.