how to map a domain with both www & non-www version

Typically you can talk to your host about your domain resolve for both www and non-www, and often there are GUI tools in your Control Panel to accomplish this.

I would recommend speaking to your host, of you can take a look here :
https://htaccessbook.com/htaccess-redirect-https-www/
https://www.siteground.com/kb/how_to_redirect_nonwww_urls_to_www/

You need reWrite Rules in your htaccess file.

I have tried the htaccess rewrite rule but it doesn’t work.

Due to the multisite setup, I need to add the domain as Alias (formerly known as Parked Domain) in cpanel. Then in the wordpress multisite site url, I will have to change it to the said domain.

Here’s the problem with wordpress multisite mapping:

If in site’s URL, I put it as https://subsite-domain.com (without www), it works perfectly, even if someone key in https://www.subsite-domain.com (with www), they will get 301 redirected properly to https://subsite-domain.com.

However,
if I put in site’s URL as https://www.subsite-domain.com (with www this time), then when someone key in https://subsite-domain.com (without www), instead of they get redirected to https://www.subsite-domain.com, they will get redirected to wordpress multisite primary domain, where I install wordpress multisite.

Anyone encounter such problem?

Enable mod_rewrite. Open terminal and run the following command to enable mod_rewrite on Ubuntu/Debian systems.
Enable . htaccess in Apache Server.
Create .htaccess file. Open terminal and create .htaccess file $ sudo vi /var/www/html/.htaccess.
Redirect www to non-www in Apache htaccess.
Restart Apache Server.

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