"Allow bookings with registered emails" does not works on demo version,
I would like to buy it but first I have to fix it.
This is the configuration that I have set in order to not have duplicate emails
Allow guest bookings - YES
Allow double bookings -NO
Enable No-User Booking Mode - NO
Allow bookings with registered emails - YES
Otro camino seria buscar otro plugin, pero este me gusta mucho por su integración con WPML.