Problem with a client requesting a TCP service about resty HOT 4 CLOSED

_httpClient = resty.NewWithClient(&http.Client{Transport: http.DefaultTransport})

_httpClient = resty.New()

package main

import (
	"fmt"
	"io"
	"net/http"
	"strings"
	"sync"
	"time"

	"github.com/go-resty/resty/v2"
)

func main() {
	url := "http://0.0.0.0:23360"
	method := "POST"

	payload := strings.NewReader(`Hi`)

	req, err := http.NewRequest(method, url, payload)

	if err != nil {
		fmt.Println(err)
		return
	}
	req.Header.Add("Content-Type", "text/plain")
	req.Header.Add("Connection", "close")

	res, err := httpClient().GetClient().Do(req)
	if err != nil {
		fmt.Println(err)
		return
	}
	defer res.Body.Close()

	time.Sleep(2 * time.Second)

	body, err := io.ReadAll(res.Body)
	if err != nil {
		fmt.Println(err)
		return
	}
	fmt.Println("Response from server:", string(body))

	// Resty Code
	resp, err := httpClient().R().
		SetHeader("Content-Type", "text/plain").
		SetBody(strings.NewReader(`Hi`)).
		SetContentLength(true).
		Post(url)
	fmt.Println("Resty code, response from server:", resp, err)
}

var _once sync.Once
var _httpClient *resty.Client

func httpClient() *resty.Client {
	if _httpClient == nil {
		_once.Do(func() {
			_httpClient = resty.NewWithClient(&http.Client{Transport: http.DefaultTransport})
			// _httpClient.SetTimeout(_defaultHTTPRequestTimeout)
			// _httpClient.JSONMarshal = sonic.Marshal
			// _httpClient.JSONUnmarshal = sonic.Unmarshal
			_httpClient.SetPreRequestHook(func(c *resty.Client, req *http.Request) error {
				req.Close = true
				return nil
			})
		})
	}
	return _httpClient
}