How to configure Multiple Domain at the same site ID using multi site setting

So you want to map multiple domains to the same WordPress site?

You might want to look for “multiple domains” in the plug-in directory:
https://wordpress.org/plugins/search/multiple+domains/

multi site sub directories

You can do this with WordPress multisite network.

https://wordpress.org/support/article/create-a-network/
https://wordpress.org/support/article/before-you-create-a-network/#types-of-multisite-network

The sites in a network have different URLs. You can choose one of two ways for the URL to specify the site:

Each site has a different subdomain. For example: site1.example.com, site2.example.com.
Each site has a different path. For example: example.com/site1, example.com/site2

https://www.wpbeginner.com/wp-tutorials/how-to-install-and-setup-wordpress-multisite-network/#customdomain

so I have tried duplicating DB and contents and it worked well.
I will go ahead with this way.

Good to hear.

I have these 2 sites.
example.com/mySite1
example.com/mySite2

And I want to show example.com/mySite1 as mydomain.net/mySite1 too.
How about in this case?
I could not find any solutions.

There is a standard solution to this. I’ll describe here in case other users who may be reading this thread.

This method is the primary way to solve your problem; it’s simpler and less problematic than duplicating DB and contents. You don’t need to duplicate DB and contents just to solve this.

You basically redirect the DNS records of mydomain.net to your web server and set mydomain.net as your WordPress site URLs.

1.) With your domain registrar, set the DNS A record of mydomain.net to your web server. Then, configure your web server listen for mydomain.net (you can do this with software such as cPanel).

2.) Set mydomain.net as your WordPress site URLs:

edit WP_HOME and WP_SITEURL according to this guide:
https://wordpress.org/support/article/changing-the-site-url/#edit-wp-config-php