admin/mdeploy/notwritable

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

The exact directories depends on the type of plugins. For example Moodle activities are stored in the /mod directory. For a full list of directories see the Moodle path on https://docs.moodle.org/dev/Plugins

See also more about Installing plugins.