Shutterstock – lightboxes – Missing required scope error

I am trying to get my lightbox-collection of images from shutterstock. I am using php (wordpress site). For that I followed examples in documentation, but applied the code for my app.

To get token I use this code:

$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;
  }

After that to get lightbox I go with this code:

…

$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);

However, instead of request with lightbox info, I get this error:

Missing required scope: collections.view

As you see I have scope parameter in my parameters array. What am I missing there?