Welcome to GPLDL - we are still beta - please report any bugs via the contact form.
https://theeventscalendar.com/support/forums/topic/to-begin-using-event-tickets-plus-please-install-and-activate-the-latest/
To begin using Event Tickets Plus, please install and activate the latest version of Event Tickets and ensure its own requirements have been met
I also can not use the plugin, following :(