Using personal registration links prevents double registrations. However, if you need to use the event's open registration link and you wish to avoid double registrations, you can modify the event's settings so that a given e-mail address can only be used once for registration.
To enable this setting, go to your event and in the left menu, click Registration page and modify the E-mail question. Click Advanced settings > What can participants do? > Only one registration with the same e-mail address allowed. Save.
Note! Please do not use this feature in events where both the open and personal registration links are in use. If invitations are sent from Lyyti, but the open registration link is published e.g. in the newspaper or social media, it is possible that someone that has received an invitation with their personal registration link tries registering via the open registration link. In this case the registration would not be successful because their e-mail address has already been added to the event's list of invitees (=not reacted participants), and Lyyti will prevent this attempt of double registration through the open registration link.