This interface contains the required methods (if any) from the protocol defined by StoreKit.SKPaymentTransactionObserver.

If you create objects that implement this interface, the implementation methods will automatically be exported to Objective-C with the matching signature from the method defined in the StoreKit.SKPaymentTransactionObserver protocol.

Optional methods (if any) are provided by the StoreKit.SKPaymentTransactionObserver_Extensions class as extension methods to the interface, allowing you to invoke any optional methods on the protocol.