Group::isMember

static function isMember(int $groupId, int $userId): bool
{
	if (!Loader::includeModule('tasks'))
	{
		return false;
	}

	if (!Loader::includeModule('socialnetwork'))
	{
		return false;
	}

	if ($groupId <= 0)
	{
		return false;
	}

	return \Bitrix\Tasks\Integration\SocialNetwork\Group::getUserPermissionsInGroup($groupId, $userId)['UserIsMember'];
}