How can I write to a socket accepted from a tcp listener?

I´m working on Unity app that can be remote-controlled via an iOS app. The Unity app has got a tcp listener, that handles the incoming data. That works fine so far.

Now I want Unity to send a response to the iOS app. I´ve tried several approaches like sending bytes to the socket, creating a NetworkStream ... Nothing worked. Here´s my unity c# code:

     void Receive() {
         print ("Hello world");
         try{
             tcp_Listener = new TcpListener(IPAddress.Parse(ip), 8082);
             tcp_Listener.Start();
             print("Server Start: "+ip);
         }catch(Exception exc){
             Debug.Log("ecx: "+exc);
         }
         while (mRunning) {
             //check if new connections are pending, if not, be nice and sleep 100ms
             if (!tcp_Listener.Pending()){
                 Thread.Sleep(100);
             }else {
 
                 Socket ss = tcp_Listener.AcceptSocket();
 
                 byte[] tempbuffer = new byte[10000];
                 ss.Receive(tempbuffer); // received byte array from client
 
                 var str = System.Text.Encoding.Default.GetString(tempbuffer);
 
                 Loom.RunAsync(()=>{
                     Loom.QueueOnMainThread(()=>{
                         parse(str); 
 
                     });
                     
                 });
 
                 // send response
 
                 string data = "hallo";
                 byte[] bytes = System.Text.Encoding.UTF8.GetBytes(data);
 
 
                 ss.Send(bytes);
                 ss.Close();
 
                 Debug.Log("sending: "+System.Text.Encoding.UTF8.GetString(bytes));
 
             }
         }
     }

The string "hallo" is never written to the output.

What am I doing wrong?

Thanks very much in advance, K.