支付验证签名支付失败？—— 微信支付的app支付

$wx_result = $wechatAppPay->unifiedOrder( $params );//调用同一下单接口，并成功返回结果
 
//开始生成二次签名
$sign_array              = array();//第二次签名需要的参数
$sign_array['appid']     = $wx_result['appid'];
$sign_array['mch_id']    = $wx_result['mch_id'];
$sign_array['prepay_id'] = $wx_result['prepay_id'];
$sign_array['nonce_str'] = $wx_result['nonce_str'];
$sign_array['timeStamp'] = time();
$sign_array['package']   = $wx_result['Sign=WXPay'];
$sign_two = $wechatAppPay->MakeSign($sign_array);//调用签名生成函数

/**
 * 生成签名
 *  @return 签名
 */
public function MakeSign( $params ){
    //签名步骤一：按字典序排序数组参数
    ksort($params);
    $string = $this->ToUrlParams($params);//调用拼接函数
    //签名步骤二：在string后加入KEY
    $string = $string . "&key=".$this->key;
    //签名步骤三：MD5加密
    $string = md5($string);
    //签名步骤四：所有字符转为大写
    $result = strtoupper($string);
    return $result;
}
      /**
     * 将参数拼接为url: key=value&key=value
     * @param   $params
     * @return  string
     */
    public function ToUrlParams( $params ){
        $string = '';
        if( !empty($params) ){
            $array = array();
            foreach( $params as $key => $value ){
                $array[] = $key.'='.$value;
            }
            $string = implode("&",$array);
        }
        return $string;
    }

$notify_url        = 'http://www.XXXXXX.com/index.php/apps/cart/wxResult';

//微信支付回调函数
public function wxResult()
{
    $data = array();
    $data = $this->wechatAppPay->getNotifyData();//调用获取数据函数
    
    ////////********逻辑处理********//////////
    
 $data2 = $this->wechatAppPay->replyNotify();//接收通知成功后应答输出XML数据
 
 
 $this->jsonmsg($data);
 }

/**
 * 
 * 获取支付结果通知数据
 * return array
 */
public function getNotifyData(){
    //获取通知的数据
    $xml = $GLOBALS['HTTP_RAW_POST_DATA'];
    $data = array();
    if( empty($xml) ){
        return false;
    }
    $data = $this->xml_to_data( $xml );
    if( !empty($data['return_code']) ){
        if( $data['return_code'] == 'FAIL' ){
            return false;
        }
    }
    return $data;
}

   /**
     * 接收通知成功后应答输出XML数据
     * @param string $xml
     */
    public function replyNotify(){
        $data['return_code'] = 'SUCCESS';
        $data['return_msg'] = 'OK';
        $xml = $this->data_to_xml( $data );
        echo $xml;
        die();
    }