User Activity

Hi! Looking for some help for creating a custom action for Asana to invite new users to a team. If any of you have an idea on how to create this it would be much appreciated!
Can anybody help me with having the workbot actually tag somebody in Slack? I've tried having it post a message with using the @, followed by the employee name, displayname, username, etc and nothing seems to actually tag the user when the message po...