on
Sets the callback function for when an offer is declined.
This method sets the onDecline event handler, which is triggered when the user declines a licensing offer. The event is triggered either when the offer flow is dismissed or when the user selects "Back Off".
Parameters
on
: The closure to be executed when an offer is declined. The closure takes two arguments: the Offer that was declined, and an optional LicenseRecord object containing the license information for the declined offer, if it was accepted before.