类未找到错误但类可用

Question

我的文件夹结构如

1）samples文件夹包含所有请求的文件

2）lib文件夹包含所有必需的类

当我运行特定文件RequestPermissionsReceipt.php文件时，显示错误

  

致命错误：未找到类'PayPal \ Types \ Common \ RequestEnvelope'   第59行的samples / RequestPermissionsReceipt.php

但此类可在lib\PayPal\Types\Common文件夹中找到。

我该怎么做才能删除此错误？我的RequestPermissionsReceipt文件的代码是

use PayPal\Service\PermissionsService;
use PayPal\Types\Common\RequestEnvelope;
use PayPal\Types\Perm\RequestPermissionsRequest;

require_once('PPBootStrap.php');

$serverName = $_SERVER['SERVER_NAME'];
$serverPort = $_SERVER['SERVER_PORT'];
$url =  dirname('http://'.$serverName.':'.$serverPort.$_SERVER['REQUEST_URI']);
$returnURL = $url."/GetAccessToken.php";
$cancelURL = $url. "/RequestPermissions.php";

$scope = array();
   if(isset($_POST['chkScope'])) {
      $i = 0;
      foreach ($_POST['chkScope'] as $value) {
          $scope[$i++] = $value;
      }
   }
$requestEnvelope = new RequestEnvelope("en_US");