wp post to pdf enhanced

I have downloaded and installed this plugin, however I am getting the following error:
Fatal error: Call to undefined function mb_detect_encoding() in /web1/user21143/website/chi-beauty/wp-content/plugins/wp-post-to-pdf-enhanced/simplehtmldom/simple-html-dom.php on line 988

Any ideas on how to resolve this?

https://ww.wp.xz.cn/plugins/wp-post-to-pdf-enhanced/