Help with vCAC extensibility and vCO

I'm trying to create a vcac/vco tandem workflow to change the name of the machine during initial build.

To do so, I've set the wfstubbuildingmachine to run after a user submits a request. I have it tied into a vCO workflow called "Generate server name." The workflow is pretty simple. It consists of the following:

in: vcacvVM(vcac:entity)

out: serverName (string)

The code is:

var domainName (this is just a custom property I created in the blueprint) = vcacVM.getProperty("Custom.Domain");

System.debug("Found domain: " + domainName);

serverName = domainName;

When this runs the out put is "Found domain: null". I have tried multiple variations of the "getProperty" (i.e. .get,, .getProperties) and nothing works. Any ideas?