http://www.landmarkgeospatial.com/ArcGIS/rest/services/Doddridge

http://www.landmarkgeospatial.com/ArcGIS/rest/services/Doddridge

This is a folder inside the services directory, not the server root. Trim back to /rest/services to connect to the whole server.

Answers over http, not https. A browser on an https page will block it as mixed content, with no error text. Server to server clients are unaffected.