Hi Vincenzo,
Thanks for your interest in Event Tickets Plus! While there’s no built-in functionality to set this type of limitation in our own plugin, by pairing Event Tickets Plus with WooCommerce for payment processing, you may be able to set this type of limitation. This forum thread provides a bit more information on how to set this up:
https://theeventscalendar.com/support/forums/topic/limit-tickets-per-user/
Of course, you’ll want to ensure that ticket sales are limited to registered users only when using this method. You can set this preference in your plugin settings.
As far as cancellations are concerned, registered users who have set RSVPs can modify or cancel their RSVPs at any time by simply logging in to their account on your site. However, paid ticket orders cannot be cancelled by the user directly–they’ll need to contact you (or another site administrator) to ensure that the order is cancelled and payment is refunded manually.
I hope that helps to address some of your concerns here! Thanks again, and let me know if you should have any other questions! 🙂