To track visitors across multiple subdomains, add a domain name parameter to $A1Config to make the user visible across subdomains:

<script>
var $A1Config = {
    key: "yourKeyHere",
    tenantId: 123,
    domain: ".mydomain.com"
};
</script>

Using an invalid domain causes the cookie to silently fail to write and that prevents CDP from tracking users on the website. In the preceding example, you must replace .mydomain.com with the correct domain.