Guest access is primarily controlled at the hub level. On such hubs, Project Administrators can choose to turn off guest access to their project. The illustrations below show how invites work on projects that allow guests and those that don't.
Invites from a Guest-enabled Project
If guest access is enabled at the Project level, invites work as shown in the illustration below.
Invites from a Guest-disabled Project
If guest access is disabled at the Project level, invites work as shown in the illustration below.
