Seatrobot calls these types of Invites 3rd Party Invites (Silver Level subscriptions and above only). In a 3rd Party Invite you invite an individual to be in charge of a group of seats or invites at your event (like a table). In their invite they receive a link to create their own login to a special page in Seatrobot where they fill those seats by inviting and confirming other people themselves. In a 3rd Party Invite therefore you invite someone to be the Coordinator for that group. This individual may not be attending the event themselves.
Tip: Note: 3rd Party Invites will only appear if you have checked the '3rd Party Invites' checkbox in Event Setup > Event Info, or if you have created a Seating Package in Event Setup > Packages / Tickets and marked it as a '3rd Party' package.
Go to Emails. You must open / edit / save all the default emails in the '3rd Party Email Setup' panel. Once done, you can click the + 3rd Party button to create a new 3rd Party invites.
You'll choose a 'Co-ordinator'. The Co-ordinator is the 3rd party contact who will be in charge of inviting / filling their guest list on behalf of your event. They will receive a Coordinator Welcome email with a link to their own page where they can fill add / invite guests into the places you have given them. (The number of places they have to fill will depend on the number of seats that were contained in the Package you added to their Invite).
For more info on 3rd Party Guest Management click here.