There are 5 different kinds of Side Hustles in the game. You must complete all instances of all of them for this trophy. They are all relatively short and show up on your map when unlocked. You often need to complete side hustles before unlocking more of that type so you'll be bouncing around the map a lot. Also note that any bonus objectives are optional but offer extra rewards if you wish to go for them. The Side Hustles are:

@TCHA - Leave a negative review on a business then defeat the faction that come after you. The lower rating you give, the more enemies that come and the higher reward you get, but feel free to give 4 stars for the easiest time.

Choplifting - Pick up the target using the magnet on a helicopter and take it to the waypoint.

Pony Express - Drive the car offroad to the waypoint avoiding or destroying enemies.

Riding Shotgun - Be the passenger or rooftop surfer for a thief, helping her survive and escape the cops.

Wingsuit Saboteur - Wingsuit from building to building destroying the targets and killing enemies in your way.

Once every Side Hustle is completed you'll get this trophy.