Epic Games, creator of the popular video game Fortnite, was struck with the Federal Trade Commission’s largest penalty ever for a rule break this week.

The developer will pay $520 million for violating the Children’s Online Privacy Protection Act as well as for luring millions of players into making unintended in-game purchases using a technique called “Dark patterns.”

Fortnite is free to play and generates billions of dollars from in-game purchases, such as digital skins for players’ characters and seasonal “Battle Passes” that provide valuable items as a user spends more time playing.

In a release breaking down Epic’s violations, the FTC said that the game’s “counterintuitive, inconsistent and confusing button configuration led players to incur unwanted charges based on the press of a single button,” including while players thought the game was in sleep mode or in a loading screen.

“These tactics led to hundreds of millions of dollars in unauthorized charges for consumers,” the FTC said.

Fortnite also allowed children to buy its in-game currency “without requiring any parents or cardholder action or consent.” Parents complained that their kids “racked up hundreds of dollars in charges before they realized Epic had charged their credit card without their consent.”

“The laws have not changed, but their application has evolved and long-standing industry practices are no longer enough,” Epic said in a statement in response to the penalty. “We accepted this agreement because we want Epic to be at the forefront of consumer protection and provide the best experience for our players.”

Of the $520 million fine, $245 million will be set aside for customer refunds.