Chat::getMembersId

static function getMembersId(int $chatId): array
{
	$ids = [];

	if ($chatId && BitrixMainLoader::includeModule('im'))
	{
		$chatRow = self::getRow($chatId);
		$users = BitrixImChat::getUsers($chatRow['CHAT_ID']);
		foreach ($users as $user)
		{
			$ids[] = $user['id'];
		}
	}

	return $ids;
}