This trophy is awarded for completing 40 Fixer contracts. There are a total of 46 Fixer contracts in the game, so you don't need to complete them all.
There are different types of contracts, including:
Transporter - requires you to transport up to three vehicles to a destination, within a specified time limit and minimising vehicle damage.
Decoy - basically a checkpoint race, you'll attract heat from the cops as you go.
Getaway - requires you to collect a vehicle, evade either the cops or gangsters, then deliver it undetected to a drop location.
Interception - requires you to either track and hack a vehicle target, then take them out, or just take them out.
You'll unlock Fixer Contracts automatically (via remote profiling) in various areas once you've unlocked CTOS towers. Completing Fixer contracts and other side missions (Hideouts, Convoys, etc) often also unlocks new Fixer Contracts.
Personally I found the Decoy and Transporter missions the easiest, Interception generally isn't too bad either but Getaway can occasionally be a bit of a pain. You only need 40 of 46 so if there's a category you particularly dislike, you can avoid it!