Oreo: LocalOnlyHotspot is created, but socket exception happens

Question

I am creating some testing app, and I need to connect several devices via Wi-Fi direct. On Android 8 the only way to do it is to create LocalOnlyHotspot. I have done it successfully, devices are connecting. However I need to transfer some strings between devices. For those reason I have made in separate threads

-> on server side

try{
        int port = 9802;
        ServerSocket serverSocket = new ServerSocket(port);
        running = true;
        while (running){
            Socket socket = serverSocket.accept();
        }
    } catch (IOException e) { e.printStackTrace(); }

-> on client side

 Socket socket = null;
    try{
        socket = new Socket(address, port);
    } catch (IOException e) { e.printStackTrace(); }

I am always getting an exception on client's side

failed to connect to /192.168.43.1 (port 9802) from /:: (port 33044): connect failed: ECONNABORTED (Software caused connection abort)

As I have googled the reason is that the network has no internet connection.

How can I solve this problem? Is any other way to pass strings between 2 devices on Android 8 using Wi-Fi direct?

Thanks in advance.