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.