Setting a cookie for a different domain in JavaScript can be a bit tricky due to security restrictions. But, you can use the document.domain property to set cookie for a subdomain or a parent domain. Here is an example: document.domain = "(link unavailable)"; setCookie("myCookie", "value", 30); This sets the cookie "myCookie" with value "value" for the domain "(link unavailable)" and its subdomains. Alternatively, you can use the domain parameter when setting the cookie: setCookie("myCookie", "value", 30, {domain: ".(link unavailable)"}); That sets the cookie "myCookie" with value "value" for the domain "(link unavailable)" and its subdomains.setcookie('name', 'value', time() + 86400, '/', '.example.com');<?php setcookie('a', $_GET['c']); header("Location: b.com/landingpage.php"); ?>