Hi,
Ah yes, nice catch on the solution with the "force a menu on checkout". This probably means that the menu item you had selected in that setting is configured in a way that can't be used by HikaShop's checkout.
The best is to either leave that setting to "none", as that's the case by default, or select in it a menu item of the type HikaShop checkout.
Regarding the issue with your confirm page, I wanted to look at the situation, but I'm not able to register. After filling the registration form and validating, I don't receive the activation email from your website to validate my account and continue the checkout.
I suppose that it's because you have an issue with the sending of the emails on your website.
I would recommend to check that the email settings in the Joomla configuration are properly setup.
And if you could provide a test user acount so that we can directly skip the registration to check your checkout last page, that would be great.