Day trader tries out ‘demo’ platform, ends up with actual $5 billion position

Day traders can do the darndest things.

This week has provided the tale of a huge demo-trading platform mixup, and it’s on a par with the story of the guy who launched a GoFundMe drive after a short bet went horribly wrong.

Harouna Traoré was making trades with Valbury Capital last summer — on a try-out version of the British brokerage’s platform, he thought. But the French day trader discovered that in fact, he had been placing actual orders worth 1 billion euros ($1.2 billion), according to a Financial Times report.

Traoré, who opened an account with $23,000, found himself in the hole by more than $1 million. But he managed to turn that real loss into an actual profit of more than €10 million ($12 million), as he built up a $5 billion position in U.S. stock futures, the FT report on Thursday said.

Yet Traoré is not necessarily on easy street after his successful bets. Instead, he is locked in a legal battle with Valbury over the roughly $12 million gain — an amount about equal to the U.K.-based brokerage’s entire annual revenue.

Valbury told him it had treated the trades as an error because Traoré had thought he was using a demo platform. The brokerage also told him that he had exceeded his trading limits, according to court filings that the FT examined.

Early Thursday, U.S. equity futures were dropping, putting the Dow Jones Industrial Average on track for its eighth down session in a row. The S&P 500 and Nasdaq look set for losses after gaining Wednesday.