PHP-致命错误：找不到类'Stripe \ EphemeralKey'？

Question

我正试图为我的Stripe客户创建一个临时密钥，但是由于某种原因，我的php后端抛出以下错误？

  

致命错误：找不到“ Stripe \ EphemeralKey”类   /var/www/html/myFile.php在第21行

知道为什么会这样吗？

     <?php // Create a customer using a Stripe token

  require_once('vendor/autoload.php');

        // If you're using Composer, use Composer's autoload:

        ini_set('display_errors',1);
        error_reporting(E_ALL);

        // Be sure to replace this with your actual test API key
        // (switch to the live key later)
        \Stripe\Stripe::setApiKey("MYLIVEKEY");

        if (!isset($_POST['api_version']))
        {
           header('HTTP/1.1 400 Bad Request');
        }

        // Create Stripe Customer
        try {

            $key = \Stripe\EphemeralKey::create(array(
            "customer" => $customerId, // Convert amount in cents to dollar
            "stripe_version" => $_POST['api_version']
                )
            );

           header('Content-Type: application/json');
            exit(json_encode($key));
        } catch (Exception $e) {
            header('HTTP/1.1 500 Internal Server Error');
        }

        ?>

编辑：下面添加了Composer.json文件。

composer.json

{
  "name": "stripe/stripe-php",
  "description": "Stripe PHP Library",
  "keywords": [
    "stripe",
    "payment processing",
    "api"
  ],
  "homepage": "https://stripe.com/",
  "license": "MIT",
  "authors": [
    {
      "name": "Stripe and contributors",
      "homepage": "https://github.com/stripe/stripe-php/contributors"
    }
  ],
  "require": {
    "php": ">=5.4.0",
    "ext-curl": "*",
    "ext-json": "*",
    "ext-mbstring": "*"
  },
  "require-dev": {
    "phpunit/phpunit": "~4.0",
    "php-coveralls/php-coveralls": "1.*",
    "squizlabs/php_codesniffer": "~2.0"
  },
  "autoload": {
    "psr-4": { "Stripe\\" : "lib/" }
  },
  "extra": {
    "branch-alias": {
      "dev-master": "2.0-dev"
    }
  }
}