The invitation code is a feature designed to keep your event secure from undesirable people who may want to access your event's information.
After you upload your attendee list, your attendees can download the Whova app and sign in with their registration email address to instantly access your app without having to search for it or enter a code. If one of your attendees signs in with the incorrect email address or someone who is not on your attendee list wishes to access your app, they will have need the invitation code from the event's admins. They will also have the option to request access to the app.
Their request will send you an email stating who is trying to access your event app; you will then have the opportunity to confirm or deny them entry to your app in your dashboard under Tools > Moderator Tools > App Access Requests. If you would like to have the invitation code for your app removed completely, please contact your assigned Customer Success Specialist or email firstname.lastname@example.org.