Outside of market hours, fractional trading customers were able to create unintentional short positions by selling more shares than they own, resulting in a breaking change to prevent this issue. The change will be implemented on October 27, 2021, for live environments and October 13, 2021, for paper trading and sandbox environments, with SDKs also being updated accordingly. This adjustment aims to improve the customer experience by preventing mixed notional and quantity sell sequences outside of market hours.