php 微信授权登录 40029错误[通俗易懂]

public function getUserDetail(){ 
   
        $appid = "xxxxxxxxxxxx";
        $redirect_uri = urlencode("www.xxx你的后台入口xx.com/getUserInfo");

        $url = 'https://open.weixin.qq.com/connect/oauth2/authorize?appid='.$appid.'&redirect_uri='.$redirect_uri.'&response_type=code&scope=snsapi_userinfo&state=123#wechat_redirect';
        header('location:'.$url);
    }

public function getUserInfo(){ 
   
        $appid = "xxxxxxx";
        $appsecret = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxx";

        $code   = $_GET['code'];

        if ($_SESSION[$code]) {
  
  //判断是否已经存在，如存在直接使用code
        //先获取token
            $url = 'https://api.weixin.qq.com/sns/oauth2/access_token?appid='.$appid.'&secret='.$appsecret.'&code='.$code.'&grant_type=authorization_code';
            $res = $this->http_curl($url,'get');
            $access_token = $res['access_token'];
            $openid = $res['openid'];
            var_dump($access_token);
            //获取信息
            $url = 'https://api.weixin.qq.com/sns/userinfo?access_token='.$access_token.'&openid='.$openid.'&lang=zh_CN';
            $res = $this->http_curl($url);
            var_dump($res);
        } else {
            $_SESSION[$code] = $code;
        }
    }