By default, everyone on citysocializer is able to attend your socials.
However, as a host you have the option to limit the people who can join your social if you choose to do so, by unchecking the relevant boxes in the second step of creating a social.
For example if you uncheck 'No children' you will be stopping members who have no children from joining your social. Another example is if you chose to uncheck the 'Relationship' category then you will be preventing the members that are in a relationship from joining your social.
When a member who belongs in those categories tries to RSVP they will get a message saying that they can not join this social, but it will not let them know which category they belong to.
In order to give some sort of explanation you can add something relevant in your title or description. For example: Girls Night Out, Under 30s Bar Crawl, Singles Party etc.