olark.configure('system.allowed_domains', string);

Notes

Set which domains the chatbox will be displayed on. If your website spans multiple domains’ subdomains, you can choose which subdomains will work.

Note that chats cannot continue across top-level domains. In order for chats to go from a top-level domain to a subdomain, the top-level domain cannot be a naked domain (i.e. the URL should be http://www.example.com, not http://example.com).

Use * as a wildcard. Separate multiple domains with commas, e.g. *.yourdomain.com,*.yourotherdomain.com.

/* custom configuration goes here (www.olark.com/documentation) */
olark.configure('system.allowed_domains', '*.yourdomain.com,*.yourotherdomain.com');

You can also add subdomains on your Setup page page.