When a user customizes an eDocBuilder template, either from a Pressero site or through API communication, a unique session for that template is created on eDocBuilder. When a user is customizing an eDocBuilder template, they can click on the Cancel button, which means that the user declines to approve the session at that time.
The user can return to the same session (such as if it is in Saved for Later on a Pressero site) and approve it when they have finished their customization, and as long as that is before the session has been purged according to session life time parameters as set on the Storage > Session Lifetime area in the account.
When a user clicks on the Cancel button and leaves the session not approved, eDocBuilder will call the postback URL with the "docSessionCancelled" parameter set to true. That parameter is false if the Add or Update buttons were clicked by the user. If you are creating an integration to eDocBuilder using the API, the "docSessionCancelled" parameter should be considered when developing the behavior for your application.
So there are no "cancelled sessions" per se, but only sessions that are approved or not approved. A session that is not approved is in an open state. But sometimes the phrasing "cancelled session" is used when describing sessions on eDocBuilder that have not been approved and are open.
For more information on the eDocBuilder iFrame API interface, please see the article below.