Thanks Jorge. Made a difference.
Here's what I get when I run systemsctl start stfu (lowcase):
dvswitch@dvswitch-server:~ $ systemctl start stfu
==== AUTHENTICATING FOR org.freedesktop.systemd1.manage-units ===
Authentication is required to start 'stfu.service'.
Authenticating as: ,,, (dvswitch)
==== AUTHENTICATION COMPLETE ===
Does this look right? Do I need to enter my password to run it?
Also, after running it, the mode changes right back to DMR when I choose STFU mode.
I think I'm getting closer.....