Sending the requestNumber to VCO from VCAC

I am attempting to send the requestNumber property to a VCO workflow.  Should I just surround the requestNumber attributes in quotes in VCAC designer?  I am not foreign to sending VCAC props to VCO.  I am sending over "__api.request.id", but trying to figure out what that references.  I am trying to get the catalog request information.  I want to be able to query by the requestNumber to check up on the request passed to VCO.  I am not using ASD.

Thank you