POST to external REST service with no URL params

Hello, we are on 8.53.12.  We need to POST data to an external third party system utilizing their REST service.  The base url has no parameters. No document template is defined. The content type is application/json for the request document and the response document. I've encountered several issues and now I'm not sure how to proceed or debug this. 

I was unable to save the service operation without providing at least one URI template Index.  So on index 1, i put a "/" thinking it would be appended to the base URL. i was then able to save the Svc Op.

However, upon testing, its giving error "Failed to find URI template resource for Service Operation: URI Resource index: -1 (158,561)"