To use the Chevrolet c10 Stepside Holtzman car in Need for Speed Payback, you need to install it with the FrostyModManager program of any version. The abandoned Chevrolet mod is needed for those who could not find a car at one time.
You need to install each car one at a time, that is, you purchased Payback in the game and left. It has a cost in the store of 0 money, everything is free.