It was working perfectly, but now I am getting an error in the Alert Setting for the Mail Format free text field that says "Text may not contain spaces or tabs."
Monit 5.35.2 on OPNsense v26.1.11
Are you on 26.1.11_3 or later?
https://forum.opnsense.org/index.php?msg=269519 (https://forum.opnsense.org/index.php?msg=269519)
I am on 26.1.11_5... will update to 26.1.11_6 and see if that helps.