Gets the valid checkout options for a service's slot.
The getCheckoutOptions() function returns a Promise that resolves to the valid checkout options for the given service's slot.
To understand how getCheckoutOptions() is used in a typical booking lifecycle,
see Typical Booking Lifecycle.
The passed checkoutOptionOptions object contains the slot ID for the service. Typically, you retrieve the slot ID with the getServiceAvailability()
function.
getCheckoutOptions() returns the options available for the specified user. For example, if the user has not
purchased any pricing plans, pricing plans are not returned even if there are pricing plans associated with the service.
An object containing the information needed to identify the service for which to list the possible checkout options. Currently, you can request the checkout options using the ID of a slot.