When you receive an Invalid Server error when logging into the Chatstack iPhone app, please check the following:

Chatstack Version

The Chatstack iPhone app requires the Chatstack Server Software v3.80.  If you do not have this version installed on your web site then you will be unable to use the iPhone app.  Please check that you are running at least v3.80 of the Chatstack Server Software.  Q&A – What Chatstack version do I have installed?

Disable SSL

Try login with SSL disabled, your /livehelp directory may not be setup to work on SSL.  You can check if your Chatstack installation supports SSL within your web browser if you try visit https://www.yourdomain.com/livehelp/  You might like to also check this within the Safari browser on the iPhone as not all SSL certificates are fully supported on the iPhone