Error Image: I created a new site in my multisite environment and replaced the subdomain address for that site with its own domain. The domain records are configured correctly, but still I can’t log into the dashboard on the new site.
The multisite or network feature of WordPress has been an essential part of the core system since version 3.0. In the past, you had to access the possibilities of Multisite via plugins first, but today this feature is part of the basic framework of WordPress. With the current version, it is possible to run sites with different domains within one installation, without being limited to subdomain solutions and directories.
Important: For a setup with subdomain or individual domains, the constant COOKIE_DOMAIN must be set. Otherwise the main domain of the installation will be entered as cookie domain in ms-default-constants and the login will not work. The browser sends cookies only to the matching domain!
Solution
In the wp-config.php the line define( ‚COOKIE_DOMAIN‘, “ ); should be inserted.
To make sure that the login with defined constant is not nevertheless hindered by existing cookies, the salt keys must be regenerated and the old ones replaced with them.