Hi Ian,
I did some modification on your global configuration, and it seems to be working fine now, but the last problem that you have is that you don't have any error message because of your template. So you'll find the solution
there
:
HikaShop uses the core Joomla messaging system to display messages on your website so if you don't see any message when you don't enter correct information during the checkout process, that's probably because your Joomla template does not contain the tag to display Joomla messages: <jdoc:include type="message" />