The Wall Street giant’s systems were poorly designed and its real-time monitoring was “ineffective,” allowing the errant trade to go through, the Financial Conduct Authority said in a statement. Citigroup did not dispute the regulator’s findings and agreed to settle the claims.

The trader had intended to sell a basket of equities valued at US$58 million but made an error while inputting the order that resulted in a basket valued at US$444 billion being created instead, according to the FCA.

Citigroup’s controls did block a portion of the trade from going through, but not all of it. About US$1.4 billion worth of equities were sold across European exchanges before the trader cancelled the order.

“Some primary controls were absent or deficient,” the FCA said in its statement. “In particular, there was no hard block that would have rejected this large erroneous basket of equities in its entirety and prevented any of it reaching the market.”

The blunder sparked a five-minute selloff in the OMX Stockholm 30 Index and ultimately wreaked havoc in bourses stretching from Paris to Warsaw, wiping out €300 billion (US$326 billion) at one point, Bloomberg News reported at the time.

In 2022, the trading blunder was seen as a blow for CEO Jane Fraser, who’d been leading an overhaul of many of Citigroup’s underlying technologies and systems in order to improve the bank’s internal controls. That work has continued as the bank seeks to satisfy a pair of consent orders it entered into with US regulators in 2020.

“We are pleased to resolve this matter from more than two years ago, which arose from an individual error that was identified and corrected within minutes,” Citigroup said in a statement. “We immediately took steps to strengthen our systems and controls, and remain committed to ensuring full regulatory compliance.”

The FCA fined Citigroup £27.77 million for the blunder, while the Prudential Regulatory Authority saddled the bank with a £33.88 million penalty.