Basically, you get 2% of whatever your Underboss' current earn is, so, what you need to do is get one of your Underboss' current earn to $500,000.
The first three starting districts (Delray Hollow, River Row, and Pointe Verdun) give $100,000 when the rackets are maxed from the delivery side missions.
The Lieutenant's districts (Tickfaw Harbor, Downtown, and Barclay Mills) give $120,000.
The Capo's districts (Frisco Fields, French Ward, and Southdowns) give $140,000.
The fastest way is you need to give one of your Underbosses: starting area, a Lieutenant's area, and two Capo's areas.
I recommend going for this on your keep one Underboss alive playthrough, unlike me and you have to do three playthroughs.
I really hope my first guide helps someone, cheers.