The plugin needs an update for the most recent (at the time) updated for Rust, it has seemed to have broken it. This is the thread that I'm getting when trying to reload the plugin.

c.reload Trade
Failed compiling 'Trade.cs':
  1. The type or namespace name 'OnlinePlayersAttribute' could not be found (are you missing a using directive or an assembly reference?) [CS0246]
     (Trade 10 line 63)

Same problem