You cannot cancel a past appointment. EXACT Admin users however can mark the appointments as Failed to Attend (FTA) or Complete.

1. Right-click the appointment in the standard Appointment Book and select Cancel Appointment...

   

   (Or select the appointment and then click the Cancel button at bottom right of the appointment book)

2. When the Cancellation dialogue displays, continue as described below:

   

   NOTE: To discontinue the Cancellation (and leave the appointment as is), simply press ESC on your keyboard or click the Don't Cancel Appointment button.

3. Select a Cancellation Reason , either from the Up/Down arrows, or from the Selector:
   

   

   From the Selector you also have the option of editing and adding Reasons. 

   If the Cancellation Reason option does not display, you need to enable it at Configure > Appointment Books: [ ] Enable Cancellation reason.

4. (Optional) Type Notes about this cancelled appointment. At the bottom of the Notes text box is a brief summary of the Patient booking history. In the sample image above, the Patient over 5 years has Cancelled once and Failed to Arrive (FTA) once. 

5. Click one of the buttons:
   Clipboard: Move the appointment to the clipboard for dragging and pasting elsewhere (rebooking immediately). This appointment is not added to the Cancel List in the Cancels tab.
   Short Notice List: Move the appointment to this list for recalling the patient at short notice, and add it to the Cancels List in the Cancels tab.
   See also: https://soeidental.atlassian.net/wiki/spaces/PHS/pages/302187279?search_id=56fb0092-50ad-46a8-af6e-b9820abe9095
   Cancel List: Add to the Cancels tab. The appointment is removed from the appointment book and added to the list in the Cancels tab, from where it can be easily dragged into a new time if required.
   Do Not Rebook: Remove this patient appointment from rebooking consideration. This appointment is not added to the Cancel List in the Cancels tab, and it can only be viewed from the Patients Recall tab.
   

   

When you cancel a patient appointment, you can choose from a list of preconfigured Reasons for the cancellation, such as Sickness, Work Commitments, Transport, etc.

If there isn't an appropriate Reason code listed, you can easily create one at the time of cancellation, from within the Cancellation window.
Prerequisite for using Cancellation Reasons:

Cancellation Reasons must be enabled in Configure > Appointment Books: Enable Cancellation reason:

To configure a Cancellation Reason

1. Right-click an appointment and select Cancel Appointment...

2. Click the List selector button alongside the Cancellation Reason field to display the View Cancellation Reasons window:
   

   

3. To edit an existing reason, highlight it and click the button, to display the Edit Cancellation Reason window.
   This enables you to change the text and/or the colour, and set whether or not a note is required to be attached to the cancellation.

4. To create a new Cancellation Reason, click the +1 button to display the Add Cancellation Reason window (this is the same as the Edit window).

   

   Type an appropriate Description.

   Optionally click the Set Colour button and choose a colour for the cancellation reason then select OK > OK to exit the windows.

5. To display notes attached to cancellation reasons, select the Cancels tab, and double-click the listed appointment to open the Edit Appointment window, where you can view the Note in the Notes about this appointment area: