OK so this waitlist option reads the UTM parameters and then sends the user to the /start page, with those parameters AND and parameters that the user provides in the form (e.g. the email address is passed as URL variable). THe /start page can then read those variables and do something with them. (like use Typeform PROs capability of reading parameters and saving them in data, making some logic changes (like not having to ask for email twice). There is a script in global settings that does this parameter reading, and pops those in hidden html embed. There's also a JS element that posts the data and then redirects to the right place. See page settings.