You will need to use the web site address where the /livehelp folder is installed. For example, if the /livehelp folder is installed at www.yourdomain.com/livehelp, then you would enter www.yourdomain.com in the server field.
When Chatstack is installed as a WHMCS add-on module then your installation should be located at www.yourdomain.com/billing/modules/livehelp or similar depending on your WHMCS location. For this configuration you would then enter www.yourdomain.com/billing/modules/ in the server field.
If you have an integrated multiple installation, you can use any URL from the domains included in the integration. For example if you have integrated installations at www.yourdomain.com/livehelp and www.otherdomain.com/livehelp, you would simply choose from either of the two domains to use in the server field of desktop app sign-in window. This only applies if your multiple domain installation is using a single MySQL database. Further details regarding a multiple domain installation is available at Q&A – How can I install Chatstack within multiple domains?.