Why is the cors error not getting resolved?

cors is allowed in golang, with code like below

func Register() *echo.Echo {
	e := echo.New()
	e.GET("/swagger/*", echoSwagger.WrapHandler) // swagger 등록
	validator.RegisterValidator(e)               // 유효성검사 등록
	e.Use(middleware.Cors())  // cors 등록
......

package middleware

import (
	"github.com/labstack/echo/v4"
	"github.com/labstack/echo/v4/middleware"
)

func Cors() echo.MiddlewareFunc {
	return middleware.CORSWithConfig(middleware.CORSConfig{
		AllowOrigins:  []string{"http://localhost:3000"},
		AllowMethods:  []string{echo.GET, echo.PUT, echo.POST, echo.DELETE},
		AllowHeaders:  []string{echo.HeaderOrigin, echo.HeaderContentType, echo.HeaderAccept},
		ExposeHeaders: []string{echo.HeaderContentLength},
	})
}

However, even if I send a request from (localhost:3000) in the react project, the cors error does not stop.

func (serverInfo *ServerInfo) ServerStart() {

	var databaseSet database.DatabaseInterface = &mysql.MysqlInfo{} // Database
	databaseSet.InitDatabase()                                      // 데이터베이스를 초기화합니다
	hosts := map[string]*Host{}                                     // Hosts

	// API
	hosts[fmt.Sprintf("%v.%v:%v", "api.v1", os.Getenv(envkey.SERVER_URL), os.Getenv(envkey.PORT))] = &Host{apiV1Route.Register()}

	// Server
	e := echo.New()
	e.Use(middleware.Logger()) // 로거등록

	e.Any("/*", func(c echo.Context) (err error) {
		req := c.Request()
		res := c.Response()
		host := hosts[req.Host]

		if host == nil {
			err = echo.ErrNotFound
		} else {
			host.Echo.ServeHTTP(res, req)
		}
		return
	})

	// e.Logger.Fatal(e.StartTLS(fmt.Sprintf(":%v", os.Getenv(envkey.PORT)), "housewhale.com+3.pem", "housewhale.com+3-key.pem"))
	e.Logger.Fatal(e.Start(fmt.Sprintf(":%v", os.Getenv(envkey.PORT))))
}

I've been spending days with this issue, how do I fix it? I've tried everything I've found in the manual or google, but the cors error doesn't go away.

There was a mistake of not attaching the error, I attached the error as below and in that time the problem was solved.

Access to fetch at 'https://api.v1.localhsot:8081/auth/retoken' from origin 'http://localhost:3000' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

On the server, cors was not allowed correctly, please configure the server side to match the request

For example, if the client sends authorization data to the header, the server also allows authorization in the header. Set the necessary request like this

package middleware

import (
	"github.com/labstack/echo/v4"
	"github.com/labstack/echo/v4/middleware"
)

func Cors() echo.MiddlewareFunc {
	return middleware.CORSWithConfig(middleware.CORSConfig{
		AllowOrigins:     []string{"http://localhost:3000"},
		AllowMethods:     []string{echo.GET, echo.PUT, echo.POST, echo.DELETE},
		AllowHeaders:     []string{echo.HeaderOrigin, echo.HeaderContentType, echo.HeaderAccept, echo.HeaderAuthorization},
		ExposeHeaders:    []string{echo.HeaderContentLength, echo.HeaderSetCookie},
		AllowCredentials: true, // Add this line to allow credentials
	})
}