Sup! I think I'm on the 6 month waitlist for support from Meraki for this issue and wanted to see if anyone has found a solution. It's easily reproducible in my environment.
I'm deploying an app to a macOS High Sierra (10.13) Macbook Air with Systems Manager installed and Profiles installed. The app requires passing an argument to register it. No matter what I put into the arguments box, the argument is not included in the package deployment. Tried it with as 12.6 client, same issue.
I'm watching the log file on the client as it receives the push, then executes the standard Meraki argument to install the app, then fails as the standard argument is not including the custom argument.
FWIW, the app is Prey Project, they have documentation on enterprise deployments here: http://help.preyproject.com/article/188-prey-unattended-install-for-computers
The argument is API_KEY=foobar123 sudo -E installer -pkg prey-mac-1.X.X-xxx.pkg -target / (and yes, I've tried every variation of it).
Meraki has a page on passing arguments here:https://documentation.meraki.com/SM/Apps_and_Software/Installing_Software_on_Windows_and_Mac_Devices
The client log states: Install started: <path to install> executing in <path to install> /usr/sbin/installer - pkg '<temp directory to .pkg>' -target / Install failed for <path to target>: No API Key provided. Stopping here.
The 'executing in' line is the standard argument it will send. It's supposed to include the contents of the arguments box but it's not.