Robinhood has become one of the Covid economy’s breakout successes. Americans marooned at home binge-watched Netflix shows, went shopping on Amazon Prime, and discovered day trading on their mobile phones. “Robinhood traders” became the shorthand explanation for the frenzy of often speculative retail investing in the pandemic lockdowns. But Annie Massa reports that Robinhood is now racing to prove it can manage a simple online trading platform and overcome a reputation for poor customer service.