I think you need to be at level 15 to unlock the mode but I was playing with Hakk & Gus who are in the mid twenties. My character is still on level 13 but after a good session yesterday evening in which I also won my first race on motorbikes, parachuted a faceplant into the ground & just missed out on a 2nd place finish in a mini race, I earned 16K.
Thanks to RLLMUK I also now understand what I was doing wrong with the Simeon car quests. I was taking them to my garage to run away from the cops & that would put a tracker on them, not sure if you can remove trackers or not? Will check when next online.
Who needs to worry about next gen consoles when current gen is so much fun.