System.Net.WebException: Error: TrustFailure (A call to SSPI failed, see inner exception.)

Question

Getting following error in xamarin: System.Net.WebException: Error: TrustFailure (A call to SSPI failed, see inner exception.)

Below is my code:

            UserRepository usr = new UserRepository();
            var restClient = usr.RestClient;         //rest client code
            restClient.BaseUrl = StdAppIds.webServerUrl;
            var restRequest = new RestRequest();
            restRequest.Resource = "/GetVersion";
            restRequest.Method = HttpMethod.POST;
            var response = await restClient.ExecutePostAsync(restRequest);  //rest request