HTML Templates Not working on update

Hello,

I am using an older version of HTML Email templates as the new version is not working.

When I send out test emails it is working fine but when I book an appointment w/ Appointments+ the template is not rendering.

I am also using an old version of A+ as I need to verify it works prior to making the updates to the live server.

What could be causing the HTML email Templates not working on the update? Is it not backwards compatible?

Please let me know,
Thanks,
Judah