SOAPUI 5.7.0

I am trying to test an API that sends to a server that uses Kerberos Authentication.

I have selected SPENEGO/Kerberos authentication and supplied username, password and domain, but it still gets rejected at the server (401 Authorization required)

However if I pass the call through a web browser (while I am signed in to the company network via Kerberos) it works.

Any ideas why ?