Create new Business group with vCO workflow

I'm working on a vCO workflow that will enable members of my team to set up new teams in vCAC..

I can't seem to workout how to map the output of "Create a Machine Prefix" , which is vCAC:Entity to the Machine Prefix Input  (defaultMachinePrefix) which is  vCACCAFE:MachinePrefix.

When I try to pass the entity ID to defaultMachine prefix I get the following error: Cannot convert undefined to java.util.UUID (Workflow:Set up new vCAC User / Create a Business Group (item6)#4)

Has anyone had any success or am I trying to do something that can't be done?

Cheers