Can not send data from client to server

Question

I can't send data from the client to the server. I checked and found out that the server didn't catch the data sending event from the client, but they connected to each other. enter image description here

// server
public void startServer() {
    Configuration config = new Configuration();
    config.setPort(PORT_NUMBER);
    server = new SocketIOServer(config);
    server.addConnectListener(new ConnectListener() {
          
  @Override
  public void onConnect(SocketIOClient arg0) {
  textArea.append("One client connect \n");
}
          
          
          
}); 
  
  server.addEventListener("register", Server_Model_Register.class, new dataListener<Server_Model_Register>() {

      @Override
      public void onData(SocketIOClient arg0, Server_Model_Register arg1, AckRequest arg2) throws Exception {
          System.out.println( "data received");
              
      }

          
          
      });
      server.start();
      textArea.append("Server has start on port : " + PORT_NUMBER + "\n" );
  }

//client
public void startServer() throws URISyntaxException {
    try {
  System.out.println("start");
  client = IO.socket("http://" + IP + ":"+ PORT_NUMBER);
  client.connect();
          
  client.on(Socket.EVENT_CONNECT, new Emitter.Listener() {
      @Override
            public void call(Object... args) {
         System.out.println("Connected to server successfully.");
                  }
              }).on(Socket.EVENT_CONNECT_ERROR, new Emitter.Listener() {
      @Override
       public void call(Object... args) {
            System.out.println("Connection to server failed.");
            for (Object arg : args) {
                     System.out.println("Error message: " + arg);
                      }
                  }
              });
           
           
      } catch (URISyntaxException e) {
          error(e);
          
      }
  }

this is action button register, then press data will process and emit to server. it was print Emited to server

@Override
public void register(Client_Model_Register data) {
              
     Client_Service.getInstance().getClient().emit("register", data, new Ack() {
                  
         @Override
         public void call(Object... arg0) {
  
   if (arg0.length > 0) {
                             
        Object response = arg0[0];
                              
        if (response instanceof String) {
        String message = (String) response;
        System.out.println("Server response: " + message);
                             
    } 
          } else {
                 
            System.out.println("No response from server.");
          }
                      
  }
 });
              
 System.out.println("Emited to server");
              
          }