While creating charge with
YocoSDK.charge(), 3rd party integrators can pass an optional
receiptNumber should be unique and is up to integrators to store.
receiptNumber allows for lookup if a transaction handle is lost, due to e.g. application exit prematurely.
receiptNumber: String - A unique string set while creating a charge
completionHandler: ((resultCode: Int, result: List<PaymentResult>?, errorMessage: String?) -> Unit)? - lookup completion handler