WebAPI : Unable to access custom entity using Web API.

I am struck here badly, Have been trying different options but no use.

I have two entities and have to create an association between these two.

I have the following code to achieve this.

 var clientURL = parent.Xrm.Page.context.getClientUrl();
    var req = new XMLHttpRequest()
    req.open("POST", encodeURI(clientURL + "/api/data/v8.0/new_experiencetopgs"), true);
    req.setRequestHeader("Accept", "application/json");
    req.setRequestHeader("Content-Type", "application/json;charset=utf-8");
    req.setRequestHeader("OData-MaxVersion", "4.0");
    req.setRequestHeader("OData-Version", "4.0");
    req.onreadystatechange = function () {
        if (this.readyState == 4 /* complete */) {
            req.onreadystatechange = null;
            if (this.status == 204) {
                var accountUri = this.getResponseHeader("OData-EntityId");
            }
            else {
                var error = JSON.parse(this.response).error;
            }
        }
    };
    var experiencetopgs = new Object();
    //String Field
    experiencetopgs.new_name = Math.random()+"ExperienceGroup";
    var experienceId =parent.Xrm.Page.data.entity.getId().substring(1, 37);
    //Lookup

    experiencetopgs["new_exppgexperience@odata.bind"] = "/***_experiences("+experienceId+")"
	experiencetopgs["new_exppracticegroup@odata.bind"] = "/new_experiencetopgs("+practiceGroupId+")"
	jObj=JSON.stringify(experiencetopgs).replace(/ /g,'');
    var response = req.send(jObj);

When it comes to ***_experiences, it's not accessible, I tried to directly access this entity using web API URL.

server/.../v8.0***_experienceses

Response : 

{"error":{"code":"","message":"Resource not found for the segment '***_experienceses'.",
"innererror":{"message":"Resource not found for the segment '***_experienceses'.",
"type":"Microsoft.OData.Core.UriParser.ODataUnrecognizedPathException",
"stacktrace":"at Microsoft.OData.Core.UriParser.Parsers.ODataPathParser.ParsePath(ICollection`1 segments)\r\n   at Microsoft.OData.Core.UriParser.Parsers.ODataPathFactory.BindPath(ICollection`1 segments, ODataUriParserConfiguration configuration)\r\n   at Microsoft.OData.Core.UriParser.ODataUriParser.Initialize()\r\n   at System.Web.OData.Routing.DefaultODataPathHandler.Parse(IEdmModel model, String serviceRoot, String odataPath, ODataUriResolverSetttings resolverSettings, Boolean enableUriTemplateParsing)\r\n   at System.Web.OData.Routing.DefaultODataPathHandler.Parse(IEdmModel model, String serviceRoot, String odataPath)\r\n   at Microsoft.Crm.Extensibility.OData.CrmODataPathHandler.Parse(IEdmModel model, String serviceRoot, String odataPath)"
    }
  }
}