How to add an extension to mediawiki?

Question

MediaWiki

Good day!
The task is to create a wiki library and its subsequent filling and optimization, but immediately ran into the problem of connecting extensions (extensions).
In particular, you need to add the extension https://www.mediawiki.org/wiki/Extension:Add_HTML_...
I did everything according to the instructions: I filled in the folder with the extension in "/extensions/", added the line

require_once "$IP/extensions/AddHTMLMetaAndTitle/AddHTMLMetaAndTitle.php";

to the LocalSettings.php file... but when the page is updated on the site, the message "Server Error" is displayed, and in general everything stops working =\
I tried to remove and change $IP to w, wiki... but something did not really help. What am I doing wrong?

Answer 1

UPD: problem solved - the plugin was not compatible with the latest version of MediaWiki