I find a plugin I want for my server and download it.  after it's downloaded I copy it and put it in the \oxide\plugin folder then in Rust Admin it says :

Could not load plugin 'Godmode' (multiple plugins with that name)

And this happens with every plugin, I have checked all of my folders and there aren't multiple anywhere to be found, anyone knows how to fix this?

Godmode is not this plugin unless you renamed it to that. Make sure you do not have multiple files under your plugins folder with the same name, ex."Godmode (1).cs" and "Godmode.cs", etc.