Waiting Lists are available for Meetup Events that have a set attendee limit. To set a limit and add a Waiting List, go to the upcoming event you want to edit, and click the 'Edit' link. On the next page, scroll down to the 'RSVP Settings' section.
Choose 'Limited to X attendees' to enable the attendee limit. Then you can select Waitlist or No Waitlist.
If you select Waitlist, members will have the option to join a Waitlist in the event that the Meetup becomes full.
Waitlists automatically add people to the Meetup in the order in which they joined to the Waitlist.
When you select No Waitlist, if a Meetup is full, members will have the option to receive alerts when a spot in the event opens up, by clicking the 'Notify Me' button.
Pick the option that's right for your Meetup Group, and click Change Details at the bottom of the page to save your changes.