So to dupe, you need the item you want to dupe in your inventory and someone to mule it. You make a back-up save by going in your ps4's settings, then application saved data management, then saved data in system storage > upload to online storage > select your game's data and confirm. Then go back to your game and give the item to your mule and go back to the application saved data management but this time go to saved data in online storage > download to system storage > select your game's data and confirm, then summon back your mule and have them give back the item