I suppose that problem should be here:

AJAX post is sending to url: https://d.websupport.sk/kontrola-objednavky and gets redirect to https://it10d.websupport.sk/kontrola-objednavky.
I suppose that AJAX should be send to: https://d.websupport.sk/www.trapez.sk/kontrola-objednavky.
But, when I try to manually send this AJAX request to url: https://d.websupport.sk/www.trapez.sk/kontrola-objednavky I get HTTP/403 error code.