Plugin not supported

I am new to WordPress and having troubles using this plugin.

When I search File Manager on plugin list, it says plugin is not supported (my wordpress version is supported, though).

It would still allow me to download it, but activation is disabled.

My guess is that I need to set up some permissions in order for File Manager to write to my website’s file system. I am using WordPress hosting service, and have set up and have access to SFTP. Can anyone help me resolve this issue?

Thanks in advance.