I think you are messing two things up here.
The configuration screenshots you sent are for webservice configuration. You need that one when you want to use a webservice (programmed by you) as a workflow step in workflow designer.
The REST API is available via the platform service ( http://docuwareServer/docuware/platform ). You do not need to set a specific configuration or anything, platform service is always available.
Did you already have a look at the developer documentation? Documentation
Greetings from Germany,
Simon H. Hellmann
DocuWare System Consultant