billingAddressParameters - Configure additional fields to be returned for a requested billing address.
existingPaymentMethodRequired - If set to true, then the isReadyToPay() class method will return true if the currentviewer is ready to pay with one or more payment methods specified inallowedPaymentMethods.
isEmailRequired - Set to true to request an email address.
merchantInfo - Merchant name encoded as UTF-8. Merchant name is rendered in the payment sheet.In TEST environment, or if a merchant isn't recognized, a “Pay Unverified Merchant” message is displayed in the payment sheet.