What VSI would be used with your VSM? What about a config file? Dependent data?
VSM + VSI + config + dependent data is what you need to deploy.
VSM + VSI + config + dependent data is what is in a MAR file.
That's why VSEManager is expecting a MAR file.
From Workstation, right-click your VSM and create a "MAR Info" from it. The MARI is a simple manifest file that lists the VSM, VSI, config and dependent data.
Right-click the MARI file and select "Create MAR". Then you have your MAR file, for storage in an object repository such as Artifactory, and for deployment through VSEManager.
If you're trying to do this without any Workstation involvement, you will need to create your manifest file yourself, and then use the MakeMar command-line utility.