tell me step by step

You’re talking about setting up a redirect domain, correct? And is it a 404 page from your site or a generic error?

Let’s say I have a site at example.com, and I want to add example.net as a redirect; visiting it will immediately change to the .com version.

1) Ensure that example.net is set to point to the same server as example.com via DNS settings; make sure the IP address is the same.

2) Ensure your server is setup to accept traffic from that domain. With a simple redirect domain you technically don’t even need this plugin, just configure it in cPanel/Plesk instead.

At this point, see if the domain redirects to your network’s main site. It should be routing to the wordpress install, and WordPress is redirecting to the official domain the site uses.

3) In WordPress go to My Sites > Network Admin > Domains and click Add New

4) Fill out the form and hit Save Changes. This is mostly needed if example.com isn’t the default site on your network.

sorry, i want set my domain alias not redirect domain, i want when i visit example.net then site show example.com/site1/ not redirect to example.com/site1/
im already set example.net set to point to the same server as example.com via DNS settings; im sure the IP address is the same.
i use this plugin for hide the real url site with my other domain.

Okay, same steps should apply though.

Are you getting a 404 that looks like it’s on your site (compare with example.com/site1/404)? If not then it’s pointed to a shared hosting system and not pointing to your account.