User DOMAIN for Service Desk Plus API

User DOMAIN for Service Desk Plus API

I am using the Servlet approach to adding a new request into Service Desk Plus.
 
Here is my string: https://assist.optimation.co.nz/servlets/RequestServlet?operation=AddRequest&username=username&logonDomainName=ONZ&password=password&requester=TestName&subject=TestSubject
 
I am getting the following error:
 
Failure Please specify the DOMAIN to which the user belongs to
 
What is this error reffering to, and where can I get the value of the DOMAIN?