TCP Conncection wait for the respons in Flutter

Future<String?> sendAndReceiveCommand(String value) async {
  try {
    final ipParts =
        '192.168.4.1'.split('.').map((part) => int.parse(part)).toList();
    final ipAddress =
        InternetAddress.fromRawAddress(Uint8List.fromList(ipParts));

    final socket = await Socket.connect(ipAddress, 80,
        timeout: const Duration(seconds: 10));

    socket.setOption(SocketOption.tcpNoDelay, true);

    final completer = Completer<String>();

    String answer = '';
    socket.listen((data) {
      answer = ascii.decode(data);
      print(answer);
      if (!completer.isCompleted) {
        completer.complete(answer);
      }
    }, onDone: () {
      socket?.destroy();
    }, onError: (e) {
      if (!completer.isCompleted) {
        completer.complete('Error');
      }
      socket?.destroy();
    });

    await Future.delayed(Duration(milliseconds: 200));
    final command = 'Value:02d11d61d03d*';
    socket.add(ascii.encode(command));
    await socket.flush();

    final response = await completer.future.timeout(
      const Duration(seconds: 5),
      onTimeout: () {
        return 'Timeout';
      },
    );

    return response;
  } catch (e) {
    return null;
  }
}

In this code, I have successfully received data from the device, but unfortunately, I am struggling with returning data. I got a "Future already completed" error. How can I return data received from the device?

The output:

DATA : 02d15d55d1,0,0,0,0,0,00,0,01,00,90,0900,9999,9999,9999,9999,9999,9999,00,00,V208,03d
Timeout