Error sending PHP request, C #

I am developing an application in C # that connects to a web service but when I try to send the data via POST I get an error in my application in C #:

  

System.Net.Http.HttpRequestException: Error sending the request.   --- > System.Net.WebException: Connection is terminated: Unexpected sending error. --- > System.IO.IOException: Can not write   data of the transport connection: The interruption of the   an existing connection by the remote host. --- >   System.Net.Sockets.SocketException: The interruption has been forced   an existing connection by the remote host

But there is something even more important when I send the data via Postman in RAW the data is sent correctly.

Here I send the data to the service

 //crear la Instacia del Api
            ApiServices api = new ApiServices();


            //Envia las Modalidades
            var Modali = manager.Getdata("Select * , descrip as Modalidad from modalidades with(nolock) ");
            if (Modali.Rows.Count > 0)
            {

                //Inserta los Clientes en el Servidor
                var data = JsonConvert.SerializeObject(Modali);
                var data1 = JsonConvert.DeserializeObject<List<Modalidades>>(data);
                var serial = JsonConvert.SerializeObject(data1);
                await api.Post(serial, "", "Cuentasporcobrar/EnviarModalidades/590025");
                               EscribirLinea("Insertó los Datos de la modalidades en el Servidor");

            }

this is the code that sends the POST request

    public async Task<bool> Post(string Data, string token, string Controler)
    {
        try
        {

            var Cliente = new HttpClient
            {
                BaseAddress = new Uri(configuracion.ServicioRest )
            };

            Cliente.DefaultRequestHeaders.Accept.Clear();
            Cliente.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
            StringContent content = new StringContent(Data, Encoding.UTF8, "application/json");
            var Url = string.Format("{0}", Controler);
            var Respuesta = await Cliente.PostAsync(Url, content);

            if (!Respuesta.IsSuccessStatusCode)
            {
                return false;
            }

            return true;

        }
        catch (Exception)
        {

        }

        return false;
    }

NOTE: This works correctly when I use my local Xamp server