org.alfresco.web.api.APIException: Failed to process format 'html' caused by: org.alfresco.service.cmr.repository.TemplateException: Error during processing of the template 'Expression service.defaultFormat is undefined on line 21, column 175 in Services_view_html.ftl.'. Please contact your system administrator. caused by: freemarker.core.InvalidReferenceException: Expression service.defaultFormat is undefined on line 21, column 175 in Services_view_html.ftl.
I believe there is a bug in the 2.0 release with that service url - the REST API was only really in preview for 2.0, if you download a nightly build or checkout HEAD code then the url will work.