You can invite anyone to a meeting in Thread. Your invitees don't need to have a Thread login to join a meeting. Follow these steps to invite someone to a Thread Meet:
How to invite someone to a Thread meet once a Meet has started.
1. Click on either of the available "Invite" buttons
2. Invite someone to your meet by entering their email address or searching your contacts and click "invite"
3. When a user accepts your meeting invitation they'll show up in the "Participants" section of the meet (any invited users who have not accepted the meeting invitation will be under the "Invited" section)