Why is the server returning 404 and not redirecting?

Question

Apache HTTP Server

I have a website, it used to be hosted by SprintHost. I decided to switch to a more interesting and powerful one. The migration was successful. But there were problems that I could not solve, most likely due to my lack of competence.

And so, there is a site, let's say mysite.ru, and there are 2 domains (1site.ru and 2site.ru), which are needed to redirect to the site mysite.ru.
If you follow the link 1site.ru, then the redirect is successful and everything works as it should.
If you follow the link 2site.ru, then the following error appears:

Forbidden

You don't have permission to access / on this server.

Apache/2.4.6 Server at www[dot]2site[dot]ru Port 80

or such

Not Found

The requested URL /post/412342/ was not found on this server.

Apache/2.4.6 Server at www[dot]2site[dot]ru Port 80

Redirect set up via .htaccess
One of the clients with whom we communicate solved the error by replacing his ip with another one. I changed the Kazan ip to Moscow, and the redirect from 2site.ru to mysite.ru was successful and everything worked.
But I don't know how to solve this problem. It confuses me that the redirect from 1site.ru works as it should, but from 2site.ru it gives errors. What can be done? And with what it in general is connected?
The server is running centOS and Virtualmin.