Fatal Error — Call to undefined function get_related_posts_thumbnails()

I installed this plugin on my wordpress website but as soon as I add get_related_posts_thumbnails() to single.php I get this error:
Fatal error: Uncaught Error: Call to undefined function get_related_posts_thumbnails() in /var/www/vhosts/dev.net/public_html/wp-content/themes/1page-wp-child/1page-wp-child/single.php:307 Stack trace: #0 /var/www/vhosts/dev.net/public_html/wp-includes/template-loader.php(106): include() #1 /var/www/vhosts/dev.net/public_html/wp-blog-header.php(19): require_once(‘/var/www/vhosts…’) #2 /var/www/vhosts/dev.net/public_html/index.php(17): require(‘/var/www/vhosts…’) #3 {main} thrown in /var/www/vhosts/dev.net/public_html/wp-content/themes/1page-wp-child/1page-wp-child/single.php on line 307

Apparently, i’m not alone:
https://www.google.com/search?sxsrf=ALeKk03CfKcLGAP8TnAXgq6YrEslSQyRBw%3A1599958578164&ei=Mm5dX5rWCaiw_Qa9yqCABA&q=%22Call+to+undefined+function+get_related_posts_thumbnails%28%29%22&oq=%22Call+to+undefined+function+get_related_posts_thumbnails%28%29%22&gs_lcp=CgZwc3ktYWIQAzoECCMQJzoHCCEQChCgAVDlM1iaQmCiRWgAcAB4AIABsAGIAYUDkgEDMS4ymAEAoAEBqgEHZ3dzLXdpesABAQ&sclient=psy-ab&ved=0ahUKEwiat9OV9uTrAhUoWN8KHT0lCEAQ4dUDCA0&uact=5