Help with Bookings by Zingiri

I am looking for someone who knows "bookings by zingiri". If you do you'll know what I'm talking about.
If you are familiar with it, I have a little glitch with it. In a nutshell, (testing 25th December) once person 1 has booked a day then it greys out, it won't then let me book for person 2. I want to run one off art classes with 4 to six people.
I've changed one thing at a time, then changed it back (like a fair test) (also try to load person 2 on different device) methodically but nothing has worked. I've spent hours on it. Meanwhile I'm nor able to book anyone through the website.
www.becomeadabhand.co.uk