This is the email sent to waiting list users of an event when a registration for that event cancelled (by the registrant or by admin of the website). The purpose is informing them so that they know that there are a space available and can join the event again.
Go to Events Booking -> Emails & Messages, look at Waiting List Messages tab, find and change the two messages below: Waiting List Notification Email Subject, Waiting List Notification Email Body to meet your need
[REGISTRANT_FIRST_NAME] : First Name of the registrant who cancel registration [REGISTRANT_LAST_NAME] : Last Name of the registrant who cancel registration [EVENT_LINK] : Link to the event (you can access to that link to see event details page and perform registration from there) [EVENT_TITLE] [EVENT_DATE] [EVENT_END_DATE]
[FIRST_NAME] : First Name of the waiting list user who the email is sent to. [LAST_NAME] : Last Name of the waiting list user who the email is sent to.