I am trying to create a Chatter post from a visual workflow.  When an Oppty is won, I want to create a Chatter post congratulating the Oppty owner and have it come from their Manager.  So far I can I can do all that using the Create Record Action


The issue I am running into, I want to @mention the Manager (so they know they "sent" a chatter post) so I created a text body formula:
 
but the Chatter post is listing the id, and not doing a true @mention


Any ideas on how to do a proper @mention via a formula?

Thanks, 

Todd B.