I can't Create a new Site - Unknown Error

[marioapplication]

I am trying to create a new site.
I complete every field and when i click "CONTINUE" it shows and error
Full error Message :"Unknown error, if the problem persists inform us through the community forum explaining which action caused this error, or write us"
https://aa.altervista.org/message.php?error=0



What should I do?

Yup, same thing had happened to me. Haven't got those screenshots, or any logs, unfortunately! :( Was only able to deal with it, with help from a friend; was not able to resolve it myself, just btw.

Windows 10 LTSB and the latest Firefox, connecting through a cable ISP, via a router...