Pretty self explanatory. You must complete the 2nd online heist (All setups and finale). This can be done on any difficulty but if you want the best payout, complete on hard.
*** Spoiler - click to reveal ***Quick tip for those having trouble avoiding the fighter jet's missiles, fly towards the jets then fly behind them as they go past you.
If you're in need of a 4th person, I'm always willing to help as long as you make fair payouts and I'm not streaming/broadcasting.