The UK's Financial Conduct Authority (FCA) has fined Citigroup Global Markets Limited (CGML) £27.76 million for failures in its systems and controls, which led to the unintended sale of $1.4 billion worth of stocks on European markets.

On May 2, 2022, a CGML trader intended to sell a basket of stocks worth $58 million. However, an input error occurred when entering the basket of stocks into the order management system, generating a basket worth $440 billion.

CGML's control systems blocked trades worth $255 billion from proceeding but did not stop the remaining trades worth $189 billion. The selected algorithm aimed to sell a portion of the total order in the market over the rest of the day.

Before the trader could cancel the order, $1.4 billion worth of stocks had been sold across European exchanges. This caused some European indices to experience a short-term sharp decline for several minutes.

Although parts of CGML's trade control framework operated as intended, some key controls were missing or inadequate. Specifically, there was no hard block mechanism to completely reject such a large erroneous basket of stocks and prevent any stocks from entering the market.

Due to a design flaw, the trader was also able to manually override pop-up alerts without scrolling down to read all the alerts. The company's insufficient real-time monitoring meant that internal alert escalation regarding the erroneous trades was too slow.

CGML did not dispute the FCA's findings and agreed to settle, qualifying for a 30% discount. Without this discount, the FCA's fine would have been £39.666 million.