Which Elgg version?
Possible causes of your issue:
1 - Make sure you've installed the plugin correctly:
/mod/plugin_id/elgg-plugin.php
You can find plugin_id in the manifext.xml (Elgg 3) and/or composer.json (Elgg 3/4)/
Ex., 'Blog' plugin must be placed:
/mod/blog
because in the manifest.xml:
<id>blog</id>
and in the composer.json:
"name": "elgg/blog",
Read more on the Elgg Docs.
The best way to install a plugin is to use composer.
2 - Check the read/write permissions on /mod directory on your server.
info@elgg.org
Security issues should be reported to security@elgg.org!
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