How to set up a 404 error page for Joomla 3?

Question

Joomla

Good afternoon!
Help me deal with the following problem when setting up 404 errors for Joomla 3.4.5: if you enter a non-existent address, for example, for a 2nd level directory, www.site.ru/o-nas/la-la-la, then the server returns a 404 code and "Page not found" is displayed, but if you enter a non-existent address immediately after the domain name, for example, www.site.ru/la-la-la - it gives 200 code and the main page of the site is displayed. It turns out that the 404 error does not work for non-existent pages of the 1st nesting level. What could be the matter and how is it solved? Thanks

Answer 1

Something with routing.
I tested it myself - there is no such bug. (Joomla! 3.4.8)
Works well: no route - 404.