$request = array (
  'key' => 'a3ce9d7077c177d834a402ab035022b6',
  'type' => 'stock_search',
  'page' => '1',
  'limit' => '9',
  'stock_type' => '1',
  'parent' => 'all',
  'randomize' => '0',
  'group[0]' => '178',
  'extstock' =>
  array (
    0 =>
    array (
      'id' => 1220,
      'type' => 'multiselect',
      'value' => 'Выгружать на наш сайт',
    ),
  ),
  'group' =>
  array (
    0 => 178,
  ),
);

$context = stream_context_create(
    array(
        'http' => array(
            'method' => 'POST',
            'header' => 'Content-Type: application/x-www-form-urlencoded' . PHP_EOL,
            'content' => http_build_query($request)
        )
    )
);

$response = file_get_contents('https://cleankey.intrumnet.com/functionapi/',false,$context);

var_dump($response);