In order to cancel a booking the client system has to send the booking references in a query with type attribute set to cancel.

The cancellation via API is only possibile until the day before the checkin.
If you need to cancel a booking in the same day of the checkin you have to contact the office.

<?xml version="1.0" encoding="UTF-8"?>
    <query type="cancel" product="hotel">
        <reference code="BOOK2005 000001"/>
        <booking name="2014-1241"/>

You can ask for a cancellation sending one of the two parameters returned in the track response: reference code or booking name. The response is pretty close to the feedback received during the booking stage: so it does not confirm the cancellation but it only acknowledge the reception of the cancellation request. A tracking message will confirm the cancellation in a later stage.