Because of security reasons, by default cookies are accessible only on the same domain from which they were set.
For example, if you have set a cookie on domain
example.com, you cannot get it on domain
So if you're planning to use subdomains (i.e. admin.example.com, profile.example.com), you need to set
$cookie = new Cookie([ 'name' => 'cookie_monster', 'value' => 'Me want cookie everywhere!', 'expire' => time() + 86400 * 365, 'domain' => '.example.com' // <<<=== HERE ]); \Yii::$app->getResponse()->getCookies()->add($cookie);
Now cookie can be read from all subdomains of