Problem sending a message

I've made a snippet of code that sends a message via TCP / IP with sockets from one computer to another. It works well (sends the message) if the two computers are connected to the same network, however, if I connect one of the two computers to a different wifi does not work.

I do not know if the problem is that I must open ports or if I have to put an IP different from the local one of the computer.

The code snippet is as follows:

private void Envio()
{
   //Ejemplo de IP
   IPAddress IP = IPAddress.Parse("192.168.1.40");

   TcpClient TCP = new TcpClient();
   await TCP.ConnectAsync(IP, 443);

   Stream Str = TCP.GetStream();

   if (Str.CanWrite == true)
   {
      var Mensaje = Encoding.ASCII.GetBytes("Hola");

      if (Str != null)
      {
         Str.Write(Mensaje, 0, Mensaje.Length);
      }
   }

   TCP.Dispose();
}

private void Recepcion()
{
   IPAddress IP = IPAddress.Parse("192.168.1.40");

   TcpListener TCP = new TcpListener(IP, 443);
   TCP.Start();

   MensajeB[] buffer = new byte[256];
   string Mensaje = null;

   bool Seguimiento = true;
   while (Seguimiento == true)
   {
      TcpClient TCPCl = await TCP.AcceptTcpClientAsync();
      ResultPrueba.Text = "Conectado";

      datos = null;

      NetworkStream NetStr = TCPCl.GetStream();

      int i;
      while ((i = NetStr.Read(MensajeB, 0, MensajeB.Length)) != 0)
      {
         datos = Encoding.ASCII.GetString(MensajeB, 0, i);
         ResultPrueba.Text = datos;
      }

      TCPCl.Dispose();
      if (datos.Length > 0)
      {
         Seguimiento = false;
      }
   }
}