So....
Firstly it's not just a case of dropping your plist into the right directory. Be very mindful of:
ensuring that you do a :
chown root:wheel yourplist.plist
and
chmod 644 yourplist.plist
on your plist after you've placed it into the right location
Secondly: LOG! If you're not already doing this, then include the following keys and values in your plist
<key>StandardErrorPath</key>
<string>/tmp/mylaunchdaemon.err</string>
<key>StandardOutPath</key>
<string>/tmp/mylaunchdaemon.out</string>
Thirdly: Deployment: Meraki Systems Manager looks for the bundle ID to detect whether or not an "app" has been installed successfully. Make sure you get this right to ensure SM knows that your apps have been installed