// PROMOBILE_SEO_CATEGORY_HEAD_V3
AddEventHandler('main', 'OnEndBufferContent', static function (&$content) {
    if ((defined('ADMIN_SECTION') && ADMIN_SECTION === true) || ($_SERVER['REQUEST_METHOD'] ?? 'GET') === 'POST') {
        return;
    }
    $path = parse_url($_SERVER['REQUEST_URI'] ?? '', PHP_URL_PATH);
    if (!$path || strpos($path, '/catalog/') !== 0 || !\Bitrix\Main\Loader::includeModule('iblock')) {
        return;
    }
    $path = '/' . trim($path, '/') . '/';
    $code = basename(rtrim($path, '/'));
    if ($code === 'catalog') {
        return;
    }
    $sectionName = '';
    $rs = CIBlockSection::GetList(array('ID' => 'ASC'), array(
        'IBLOCK_ID' => 26,
        'ACTIVE' => 'Y',
        'GLOBAL_ACTIVE' => 'Y',
        'CODE' => $code,
    ), false, array('ID', 'NAME', 'SECTION_PAGE_URL'));
    while ($section = $rs->GetNext()) {
        $sectionPath = '/' . trim($section['SECTION_PAGE_URL'], '/') . '/';
        if ($sectionPath === $path) {
            $sectionName = trim(htmlspecialchars_decode($section['NAME'], ENT_QUOTES));
            break;
        }
    }
    if ($sectionName === '') {
        return;
    }
    $sectionName = preg_replace('/\s+/u', ' ', strip_tags($sectionName));
    $title = 'Купить ' . $sectionName . ' в Санкт-Петербурге и Москве | PROMOBILE';
    if (mb_strlen($title) > 78) {
        $title = 'Купить ' . $sectionName . ' с доставкой по России | PROMOBILE';
    }
    if (mb_strlen($title) > 78) {
        $title = 'Купить ' . mb_substr($sectionName, 0, 40) . ' | PROMOBILE';
    }
    $description = $sectionName . ' в PROMOBILE: актуальные цены и наличие. Самовывоз в Санкт-Петербурге, доставка по Москве и России, гарантия и помощь с выбором.';
    if (mb_strlen($description) > 180) {
        $description = mb_substr($description, 0, 176) . '…';
    }
    $titleEsc = htmlspecialchars($title, ENT_QUOTES | ENT_SUBSTITUTE, 'UTF-8');
    $descriptionEsc = htmlspecialchars($description, ENT_QUOTES | ENT_SUBSTITUTE, 'UTF-8');
    if (preg_match('/<title[^>]*>.*?<\/title>/is', $content)) {
        $content = preg_replace('/<title[^>]*>.*?<\/title>/is', '<title>' . $titleEsc . '</title>', $content, 1);
    }
    if (preg_match('/<meta\s+[^>]*name=["\']description["\'][^>]*>/is', $content)) {
        $content = preg_replace('/<meta\s+[^>]*name=["\']description["\'][^>]*>/is', '<meta name="description" content="' . $descriptionEsc . '" />', $content, 1);
    } else {
        $content = preg_replace('/<\/head>/i', '<meta name="description" content="' . $descriptionEsc . '" />' . "\n</head>", $content, 1);
    }
});
<pre>[RuntimeException] 
Could not start session because headers have already been sent. &quot;/home/users/j/j2738487/domains/promobile.pro/bitrix/php_interface/init.php&quot;:701. (0)
/home/users/j/j2738487/domains/promobile.pro/bitrix/modules/main/lib/Session/Session.php:143
#0: Bitrix\Main\Session\Session-&gt;start
	/home/users/j/j2738487/domains/promobile.pro/bitrix/modules/main/lib/Session/KernelSessionProxy.php:47
#1: Bitrix\Main\Session\KernelSessionProxy-&gt;start
	/home/users/j/j2738487/domains/promobile.pro/bitrix/modules/main/include.php:151
#2: require_once(string)
	/home/users/j/j2738487/domains/promobile.pro/bitrix/modules/main/include/prolog_before.php:19
#3: require_once(string)
	/home/users/j/j2738487/domains/promobile.pro/bitrix/modules/main/include/prolog.php:10
#4: require_once(string)
	/home/users/j/j2738487/domains/promobile.pro/bitrix/header.php:2
#5: require(string)
	/home/users/j/j2738487/domains/promobile.pro/catalog/index.php:1
#6: include_once(string)
	/home/users/j/j2738487/domains/promobile.pro/bitrix/modules/main/include/urlrewrite.php:128
#7: include_once(string)
	/home/users/j/j2738487/domains/promobile.pro/bitrix/urlrewrite.php:2
----------
</pre>