Splunk REST API Post route is throwing Cannot perform action "POST" without a target name to act on .net core

Question

I am trying to create a role using splunk REST API (https://docs.splunk.com/Documentation/Splunk/8.2.5/RESTREF/RESTaccess#authorization.2Froles). The route works perfectly using postman, but when I try to invoke the same route using IServiceClient via .net core, I run in to "Cannot perform action "POST" without a target name to act on". Please let me know what other information I can provide. Have been searching on google for the error and in splunk documentation with no luck.

using (var client = _serviceClientFactory.GetServiceClient()) //client service factory returns a ServiceClient
                {
                    PostRoleRequest request = new PostRoleRequest
                    {
                        name = Const.DefaultRoleName //this is the only required param
                    };
                    
                    var response = await client.PostAsync<PostRoleResponse>($"/services/authorization/roles?output_mode=json", request);
                }

 public class PostRoleRequest
    {
        public string name { get; set; }
    }