i would love to use this but atm it does not work

the error is

Error while compiling NeedForSpeed: 'ScrapTransportHelicopter' does not contain a definition for 'thwopGainMin' and no accessible extension method 'thwopGainMin' accepting a first argument of type 'ScrapTransportHelicopter' could be found (are you missing a using directive or an assembly reference?) | Line: 242, Pos: 35