如何阅读这个facebook带领示例代码

i have made a successful login using facebook but i want to run this sample code where can i place this sample to test it

use FacebookAds\Api;
use FacebookAds\Http\RequestInterface;

$params = array(
  'user_id' => <USER_ID>,
);

$response = Api::instance()->call(
  '/me/leadgen_whitelisted_users',
  RequestInterface::METHOD_POST,
  $params);

i put it after login then i get this error Call to a member function call() on a non-object