How to add a private note to a ticket in Slack
A private note is only viewable by agents and admins, the requester of the ticket will not see it.
In Slack, if you preface a message in a thread with the :lock: emoji, it will be a private note.
In Microsoft Teams, you can select Reply and check the box for "Send as private note."
Private notes will show up yellow in the web interface:
You can also add a private note from the web by using the toggle: