Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.
validationURL is a read-only string value providing the URL from which to fetch the payment handler-specific data needed to validate the merchant.
This data should be passed into the
complete() method to let the user agent complete the transaction.