The HTML Tag Does not Work in the Support Manager template.
If you go to ...
https://docs.blesta.com/display/user/Support+Manager
You will see a designated " tag " for displaying the replies in HTML format.
It is " {ticket.details_html} " The ticket reply details in HTML
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The main issue appears to be that there is no WYSIWYG available within the Support Manger system.
SEE : https://requests.blesta.com/topic/need-a-wysiwyg-for-the-support-ticket-system