Pretty Easy Achievement To Obtain!
What you want to do is when you are in the main menu move over to the "Multiplayer" Section of the game and then go to "Unranked"
Hopefully you will see a few session's in use, click on anyone of them to "join Session" and it will give you an option to "Ready up or Spectate",
Simply Spectate the race and you will obtain a cool 20G at the end of the race!