Written by them, after I decide to take their installation service.
Hello!
What we have reviewed tomorrow is a very strange behaviour that can only be caused by some server settings of your ngix server. Unfortunately, we do not have time at this moment to test the add-on on ngix server and to deeply analyze your settings that could cause such issues. Due to this we refunded your payment. You should uninstall both XenCentral Framework and Multisite System from your server. We are sorry the product didn't work for you.
If we'll have ngix server support tested, we'll update you, so if you are interested in product you may purchase it again.
Sorry for inconvenience again.
Thank you!