Acuity will post to /custom-sidebar when appointment details are
viewed and display the result in the appointment details sidebar.
Acuity won't be able to access 127.0.0.1:8000 so you'll either
have to take our word for it, or try this on your server! Set your callback
location under the
Custom Sidebar integration.
All arguments are sent as application/x-www-form-urlencoded content.