Client would like to customize and add additional text and fields to the checkout page for Calendar Event.
The current design does not allow adding CSS or S-tags to the checkout page. The billing page (where payment is collected) for the calendar event is not accessible to LO admins or support. If you want to edit that page, it would require a services engagement.
Unfortunately, there's not a section / page that can be accessed to edit the payment / confirmation page for calendar event.