Hi there, I currently see your page like this – http://screencast.com/t/5PqypaFF the only thing different is you don’t have any widgets in the sidebar. The error message you’re seeing leads me to think that it’s trying to use Mijireh for payment, it should be using paypal.
1.You need to change the shortcode on the checkout page to [checkout_paypal]
2. You can find the checkout page by going to your “Pages” and then clicking edit on the “Checkout” page underneath the “Store” parent page.
It looks like you’ve not setup the products via cart66, you need to go in and enter the prices etc, for them to appear on the menu. A guide to do this can be found here https://support.redfactory.nl/documentation/restaurant-theme/integrating-cart66/