Once the Party has been created, click the Menu button to the left of the Party name. Select "Manage Approvals", then select "Consultants". To add a consultant, you will need their POP username. Their POP username is the username they use to log into POP 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.