Actually my issue seems to be elsewhere. (I have managed to link the variable machinevra as an Input to the "update machine tags" item.)
My current issue is in trying to get the VRA:Machine from this command in my scriptable task:
machinevra = Server.findForType("VRA:Machine","stu124"); //simplified to test
It errors out with:
Server error : ch.dunes.model.sdk.SDKFinderException: Unable to perform operation 'find('Machine', 'stu124')' on plugin 'VRA' : java.lang.RuntimeException: Host is a mandatory field. Please pass a valid host.
So I cant get a VRA:Machine type variable to pass to the update machine tags item. I do have a managed Vm in VRA called stu124