Support

If i try to use "Change administrator login directory to" option
for example to 'qwer'
and after that if I try to open domain.com/qwert
i am getting 404 page like this:

You have two different strings in your post, I assume that is just a typo.

Please clear your browser cache and site cookies and try the admin login again.

Yes it's just a typo

I did everything but it doesn't help. Also I tried to open the admin page in different browsers and in some of them for the first time but with the same result

Let's make sure we're on the same page as to how this feature is supposed to work. The actual directory name remains /administrator, you set the alias in WAF setup, "foobar" for example. Then to enter your back end, you use the address www.mysite.com/foobar and the Admin Tools plugin redirects you to the actual address www.mysite.com/administrator. The important bit is that the directory name doesn't actually change. If you did that, you would probably get a 404 error.

I did not rename anything.
I still can enter my back end using www.mysite.com/administrator if i rename main.php
in plugins/system/admintools/admintools to main-disable.php as it is written in docs but if i return it back than www.mysite.com/administrator redirect me to the front end and www.mysite.com/foobar to 404 page.

Dale,
I just want to be sure is this (see attachment) the usual joomla 404 page?

Dale, sorry
You don't need to answer to my last question. And actually i've found the reason.
i did't have .htaccess file in my root folder.
Thank you

As always, it makes perfect sense after somebody figures it out. I'm glad you got it working.

I think it should be better if AdminTools can check the htaccess in the root folder.