Additional Fields Problem with new version of Appointments +

Hi

Just upgraded to the latest version of Appointments+ and I have a problem with the additional fields setting. I have set up a "Post Code" mandatory field as I need this to show in my confirmation emails and calendar

However now when I try to make a booking I just get an error message

"Something wrong about the submitted Post Code"

I have tried deleting the additional field then readding it but still not working

Kind Regards
Kieran