How can you invite participants to a “members only” project?

Send them an email invitation through the site. In closed projects, access will be given only to participants who you have personally invited, or to participants that were added via the events interface or from the “add answer” interface. In closed projects for members only, you cannot share information on social networks, and the project will not be shown on the site homepage for other users to see. Additionally, the direct link to the project will redirect to the login screen.