TimeTonic offers the possibility for the owners or administrators of the books to display or hide the chatbox for the users. 

Example

I would like only the administrators of the book to have access to the messaging system so as to make our exchanges confidential in the eyes of the book users. 

Procedure 

To do this, nothing could be easier, go to the management of the users of the book :

Then indicate next to the profile of the concerned user if you grant access to the mailbox or not: