Email template for customer notification on ticket reply is not being used

Email template for customer notification on ticket reply is not being used

I've set up an email template for notify contact up upon receiving a reply in ticket. When I send a reply to the ticket, it is not using that email template. It just sends a normal looking email. How do I make it so that the email template is being used?

Note that this is not for a ticket template. It is just an email template. That has this variable in the body of the email template ${Cases.Recent Thread Content}