How to add new sites and map a custom domain in WordPress Multisite?

Domain mapping allows a blog on a multisite install to serve from any domain name. This way a blog does not have to be a subdirectory of the main install, or a subdomain. The WordPress Default supports Domain Mapping without Alias. Add the Domain in the blog-settings to the blog of the Network administration area.

Often is it helpful – but not necessary, to set the COOKIE_DOMAIN constant to an empty string in your wp-config.php:

define( 'COOKIE_DOMAIN', '' );

Otherwise WordPress will always set it to your network’s $current_site->domain, which could cause issues in some situations.

WordPress Core hopes to provide Domain Alias Mapping in the future, but until then you can make use of one of the following plugins:

• https://github.com/humanmade/Mercator
• https://wordpress.org/plugins/wordpress-mu-domain-mapping/