When setting up each event on the Snappic Dashboard you will be given the option to set an "Admin Passcode". This passcode will then be required before exiting the event, therefore, your guests won’t be able to exit the event unless they have the event passcode.
You can set this passcode under the "Event Options" section.
In addition to the passcode, you will also be able to enable the "Guided Access" iOS feature. This will prevent the guest from exiting the Snappic app. Follow the link to set up the iOS for Guided Access.