Can't install Admin plugin

I've installed the Clean Blog skeleton (working locally with MAMP). Now I'm trying to install the Admin Plugin.

For some reason I can't get any Terminal commands to work so I've tried installing admin manually. I'm getting the following error though...

"Call to undefined method Grav\Plugin\Login\Events\UserLoginEvent::toArray()".

Any ideas?

I have a feeling it may be because the skeleton version of Grav is old..? But I can't update as I can't get the Terminal commands to work.

Lastly - am I correct to put the contents of the grav folder in my htdocs folder, rather than the grav folder itself?

Thanks.

Have you installed "Login", "Email" and "Error" Plugins? They are dependencies for Admin.

Figured it out. I was adding the $ to Terminal commands ("$ bin/gpm install admin" instead of "bin/gpm install admin").

Thanks for the fast reply!