Is it possible to include the appointment details in the email sent to the admin when a client cancels the appointment? No you can find only the ID number and the link to the admin panel. It would be better if the email could contain the CLIENT, DATE_TIME, etc infos, as well, as in the confirmation email sent to the client. In my case the service provider can't acces the wp admin panel, only the email and now an ID number means nothing for him.
I tried to place the tags (CLIENT, etc) in the language files (.mo .po) I use, and in the subject of the confirmation sent to the admin it works, but only there. In the subject and message part of the email about the canceling it doesn't work.