Show list of related blog posts by category

I found a snippet of code online that showed an example of listing related blog posts (related by category) in random order, limit of 3, but not including the current post being viewed.

I tried the code and nothing....

If I comment out the IF statement I see related posts, but not sure how they are being sorted or if filtering is 100% correct as sort order seems to throw error. (See Below).

Code in page:

<?php

                    $categories = perch_blog_post_categories(perch_get('s'), array(
                       'skip-template'=>true, ));

                    if (count($categories)) {
                        $cat_slugs = array();
                        foreach($categories as $cat) {
                        $cat_slugs[] = $cat['categorySlug'];
                        }

                     perch_blog_custom(array( 
                         'filter' => 'postSlug',
                         'match' => 'neq',
                         'value' => perch_get('s'),
                         'category' => $cat_slugs,
                         'sort-order'=> RAND,
                         'count'=> 3,
                         'template'=> 'blog/related-cat.html',
                         'section'=> 'projects'
                      ));
                    }

?>

I turned on error checking and the sort order is undefined...

So not sure that we need IF statement anyway as it seems to work without it, but we need to fix sort order to be random.

Error:

Array
(
    [type] => 8
    [message] => Use of undefined constant RAND - assumed 'RAND'
    [file] => /xxx/public_html/xxx/project-detail.php
    [line] => 34
)

Confirming we are running the latest Blog and Perch version. PHP is getting a bit old but that should be fine yeah?

Perch: 2.7.3, PHP: 5.3.29, MySQL: 5.5.37, with MySQLi Server OS: Linux, cgi-fcgi Installed apps: content (2.7.3), assets (2.7.3), categories (2.7.3), perch_blog (4.5.4), perch_forms (1.7) App runtimes: <?php $apps_list = array( 'content', 'categories', 'perch_blog', 'perch_forms', ); ?>

Thanks for any help!