1.Start an invite only session and go to the spot in the video its thee main Los Santos Customs

2.Once there set spawn to Last location

3 leave GTA Online and head to Single Player

4.Go back to GTA online park any car of the map into Los Santos Customs Make sure there are no personal cars out of your garage and then open the xbox store

5 once the store is open you will click a or PS equivalent and as soon as it starts to load press the xbox button and sign out will work on PSN also

6 once it says you have singed out you can sign back in again this will load the prologue mission

7 When you can press start and go to Game load your normal SP save this will then put you as one of the 2 or 3 characters or mod your game save by downloading GTAV Save Editor from PSN and Xbox Versions available

GTA V save edditor

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8 Park the car outside Los Santos Customs in the position in the guide Then Join an Invite only session or get invited to one.

You may at this point be invisible to your friends but what we did as seen below in the guide is drive far away from each other then he could see me and get in to start duplicating or you can just take to your garage

Duplication. this will only work on cars without a tracker and insurance but round the back of the 400k mansion there is a parachute mission follow the super easy duplication method in the video e.g driver gets out this will start the mission passenger drives forward it duplicates car when other player quits mission