If you use WordPress multisite and can’t log in to subsites, and get the error “Cookies are blocked or not supported by your browser. You must enable cookies to use WordPress.” you can paste a small code in your wp-config.php file:

Read here about how to make it easier to run your WooCommerce stores

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define(‘COOKIE_DOMAIN’, false);

The location of wp-config.php is in the root of your WordPress install, and you can use several methods to edit that file. You can use FTP to download that file, and then uploading it again after adding the line. You can also get into the file manager in cPanel to do the changes here. You can even install a file manager plugin in WordPress and edit it from inside WordPress.

The error can occur e.g. if you use domain mapping.