Maybe you must do a $ composer update into the plugin path.

The required plugins are listed on the plugin page.

You can also see the requirements (minimum Elgg version, other plugins, plugin order) if you click on the plugin name in the plugin list in the popup that opens then. Or you can open the file manifest.xml that's included in every plugin with a text editor to see the plugin requirements.

Plugins published here on the site shouldn't require to resolve any dependencies with composer. At least I haven't come across a plugin yet that doesn't include the libs (not plugins!) that it needs. It's different if you install Elgg and 3rd party plugins with composer. But then the dependecies (again: libs not plugins) are downloaded already at installation of Elgg and the plugins.