I'm using Easy Appointments on an Elementor site, and though everything works just fine, I get an error message when booking an appointment. Everything is filled in, and when the submit button is clicked, nothing happens for a few seconds, after which an error box pops up with the word "Undefined". I haven't been able to pinpoint any structure in when or why it happens. The exact same appointment can result in either a successful booking, or the error message. Help is appreciated!