admin/mdeploy/notwritable

For Moodle to install and manage plugins automatically, you need to make certain directories writeable by the web server process. The "apache" user is common on Unix-based systems using the Apache web server.

The exact directories depends on the type of plugins. For a full list of directories see the Moodle path on https://docs.moodle.org/dev/Plugins

For example Moodle activities are stored in the /mod directory, so you might do this from a shell prompt on your server:

cd <your main moodle directory>
chown -R apache mod
chmod -R u+rw mod

See also more about Installing plugins.