code: public function fetch_sub_resource($type, $params = array()) {
  
      // Generate subresource endpoint by snipping out the
      // right part of the sub_resource_uri
      $endpoint = preg_replace('/api\/v[0-9]+\//', '',
        parse_url($this->sub_resource_uris[$type], PHP_URL_PATH));
  
      $sub_resource_params = array();
  
      // Extract params from subresource uri if available and create
      // sub_resource_params array
      if ($param_string = parse_url($this->sub_resource_uris[$type],
        PHP_URL_QUERY)) {
  
        $split_params = explode('&', $param_string);
  
        foreach ($split_params as $split_param) {
            $parts = explode('=', $split_param);
            $sub_resource_params[$parts[0]] = $parts[1];
        }
  
      }
  
      // Overwrite params from subresource uri with passed params, if found
      $params = array_merge($params, $sub_resource_params);
  
      // Get class name
      $class = 'GoCardless_' .
        GoCardless_Utils::camelize(GoCardless_Utils::singularize($type));
  
      $objects = array();
  
      // Create an array of objects
      foreach ($this->client->request('get', $endpoint, $params) as $value) {
        $objects[] = new $class($this->client, $value);
      }
  
      // Return the array of objects
      return $objects;
  
    }
docs: Fetch an object's subresource from the API
  
  @param string $type The subresource to fetch
  @param array $params The params for the subresource query
  
  @return object The subresource object