Once enabled an RSVP form will be displayed on single event pages: for best results you are encouraged to use the
restrict to logged in users option, otherwise you run the potential of dealing with spam responses and other issues.
Eventin - Easy Event Manager Plugin to Create Events, Modern Events Calendar, Multivendor Marketplace, Send RSVP, and Selling Tickets. QR Code for Attendees and recurring events are also there for you.