Grand Theft Auto's free multiplayer mode GTA Online has brought in around half a billion dollars from microtransactions according to a recent lawsuit filed against Take-Two Interactive.
In the lawsuit, it's stated that back in November 2015 Take-Two CEO Strauss Zelnick announced that nearly eight million people were still playing GTA Online weekly, two years after its initial release. It also reads that "GTA Online has the potential to achieve the greatest profit margin of any game created in the GTA franchise."
Microtransactions work so well in terms of profit for a company because, according to the lawsuit, "These purchases have nearly a 100% profit margin, subject only to nominal development costs and app store commissions."
For comparison, here is a list of games that generated over $100 million from microtransactions back in 2013, with Korean FPS CrossFire topping out at $957 million.
The success of the game's online mode is most likely to blame for Rockstar shifting their attention to the multiplayer and practically ignoring single player content. On April 12, Rockstar released two new game modes called Inch By Inch and Vapid Minivan.