Thanks Jason.
The form has some validation in it so an empty form can't be submitted. The form ist placed inside shop_kasse.php.
As far as I've been informed if there is data missing, it is the data belonging to all the fields in the form.
Thanks for the session destroy code. There are sessions that shouldn't be destroyed after order something.
How can I destroy session and cookies only for the "OrderReferenceID" and "OrderNumber" sessions?