Error-page after checkout

When I order any product, I get error-page after checkout

Hi,

I don't see an error on your screenshot.
On the left side, there is the thank you page, and on the right side, there is the cart module which is empty, and another module BKB Shop.
The CSS layout is off and the empty cart message is red (probably before of some CSS too), but that's all I see.

OK but, have you any idea why the page is so terrible ?

Hi,

I would have to look at that page to be able to say. I guess it must come from the CSS of the template. Try with the default template of Joomla and it should display normally.
I tried to look at the page to see what it could be more specifically, but after registering on your website, I wasn't able to login with the account.

OK you are right, with a default template I get no error page. Must find a solution in the CSS / Template