Domain Mapping WordPress Multisite is add a non-network top-level domain to subsite. This means a site created as subsite1.tomiup.com, can be mapped to show as domain.com. This also works for subdirectory sites, so tomiup.com/subsite1 can also appear at domain.com. Before setting up domain mapping WordPress multisite, make sure your network has been correctly set up, and subsites can be created without issues.
Before WordPress 4.5, domain mapping WordPress multisite requires a domain mapping plugin like WordPress MU Domain Mapping.
In WordPress 4.5+, domain mapping WordPress multisite is a native feature.
Map Domains in DNS
Make sure all the domains you want to use are already mapped to your DNS server. The additional domains should be parked upon the master domain.
Install SSL Certificates
Install SSL for the primary domain and use SERVER NAME INDICATION (SNI) for all other domains. Every domain should have SSL installed to ensure encrypted admin login.
Update WordPress
In the network admin dashboard, click on Sites to show the listing of all the subsites, and then click on edit for the subsite you want to map to. Our example, this is subsite1.tomiup.com.
In the Site Address (URL) field, enter the full URL to the domain name you’re mapping – https://mappeddomain.org – and click save.
Edit wp-config.php
If get error cookies being blocked when login to network subsite (or log in fails with no error message), open wp-config.php file and add this line after the other code you added to create the network:
define('COOKIE_DOMAIN', $_SERVER['HTTP_HOST']);