When “Allow public registration” in “Participant Settings” is turned on, participants can register by first entering their email address and then responding via the tokenized URL sent to that address. In this situation, if a participant wants to receive the registration email again (for example, because they lost the first email), entering the same email address again on the registration screen results in no visible action.

If the same email address is entered more than once, it would be preferable either to resend the original email or to display a message indicating that the email address has already been registered.

Resending the email as the default behavior seems reasonable. However, it might also be useful to provide an option to disallow duplicate registrations. The appropriate behavior may depend on factors such as whether a response has already been completed or whether multiple submissions are allowed. As an initial approach, resending the original email appears to be the least problematic solution.