Shutterstock-lightboxes-缺少所需的作用域错误

我正试图从shutterstock获取我的灯箱图像集。我正在使用php（wordpress网站）。为此，我遵循了文档中的示例，但将代码应用于我的应用程序。

要获得令牌，我使用以下代码：

$client_id = 'My CLIENT ID here.';
$client_secret = 'My client secret there';
$redirect_uri = (isset($_SERVER['HTTPS']) ? 'https' : 'http') . '://' . "{$_SERVER['HTTP_HOST']}" . strtok($_SERVER['REQUEST_URI'], '?');
if(isset($_GET['code'])) {
  $url = 'https://accounts.shutterstock.com/oauth/access_token';
  $params = array(
      code => $_GET['code'],
      scope => 'collections.view',
      client_id => $client_id,
      client_secret => $client_secret,
      redirect_uri => $redirect_uri,
      grant_type => 'authorization_code'
  );
  $ch = curl_init($url);
  curl_setopt($ch, CURLOPT_POST, 1);
  curl_setopt($ch, CURLOPT_POSTFIELDS, $params);
  curl_setopt($ch, CURLOPT_HTTPAUTH, CURLAUTH_ANY);
  curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
  curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
  $response = curl_exec($ch);
  curl_close($ch);
  $json = json_decode($response);
  if (json_last_error()) {
    echo '<span style="font-weight:bold;color:red;">Error: ' . $response . '</span>';
  } else {
    $_SESSION['access_token'] = $json->access_token;
  }

在那之后，为了得到灯箱，我用这个代码：

$url = 'https://api.shutterstock.com/v2/images/collections/33162025/items';
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Authorization: Bearer ' . $this->accessToken));
curl_setopt($ch, CURLOPT_USERAGENT, $_SERVER['HTTP_USER_AGENT']);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 1);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$response = curl_exec($ch);
curl_close($ch);
return json_decode($response);

然而，我没有请求灯箱信息，而是得到了这个错误：

缺少必需的范围：集合。查看

正如您所看到的，我的参数数组中有scope参数。我在那里错过了什么？