Once the Party has been created, click the Menu button to the left of the Party name. Select Manage Approvals.

Select the Consultants tab. 

To add a consultant, you will need their Sonlet username. Their Sonlet username is the username they use to log into Sonlet and it is case sensitive. Once you send the invite, they will have to accept the invite before they can add their inventory to the Party by going to the Parties screen and clicking the "Join" button to the invitation at the bottom of the list.