Robinhood Markets Inc. raised an additional $2.4 Billion From Shareholders, days after investors agreed to pump $1 billion into the online brokerage to support it in riding out a trading frenzy in talked-up stocks such as GameStop Inc. The big infusion-the $3.4 billion brought in since last Thursday is more than the company had previously increased in the eight years since its launch-gives Robinhood a cushion to cover a surge in collateral requirements stemming from the trading boost. The cash should also allow the company to remove multiple of the trading restrictions that displeased clients of the popular brokerage.The fundraising caps off the most thunderous period since Robinhood’s founding. The brokerage, with its free trades, easy to-use-app and digital confetti, surged in popularity when Americans stuck at home during the pandemic rediscovered the stock market.But the same forces that set Robinhood’s growth in motion became a liability last week, when beginner investors-captivated by gains that other traders showed off on online forums like Reddit’s WallStreetBets-flooded it with orders to buy and sell a handful of beaten-down stocks.