In US stock trading, the situation where the selling price is lower than the transaction price but cannot be executed may be caused by the following factors:

1.The impact of market order types

• Limit Order: If you are using a limit order, the order will only be executed when the price you set is reached or exceeded. If the market price is rapidly changing, even if your selling price is lower than the recent transaction price, the transaction may still not be completed due to market price changes or the order not reaching your price.
• Market Order: Unlike limit orders, market orders are immediately executed at the current optimal market price. If you use a limit order instead of a market order, even if your sell price is lower than the transaction price, it may not be executed in time due to the instantaneous change in the matching of buy and sell orders.

2.Insufficient market liquidity

• Insufficient buying orders: Even if your selling price is lower than the current price, if there are not enough buying orders in the market to match your selling order, the transaction will not be completed. This situation is more common when the market liquidity is insufficient or the trading volume of specific stocks is low.
• The depth of the order book: Sometimes, although the transaction price is higher than your sell price, the buy orders may have been filled by earlier sell orders, or the number of buy orders may not be enough to fully match your sell orders.

3.Price slippage

• Market fluctuations and slippage: When the market fluctuates violently, prices may change rapidly in a short period of time. The transaction price displayed by each transaction shows the past transaction record, but your order may not be executed due to sudden market changes, resulting in a selling price lower than the transaction price but still not executed.

4.Delayed execution and matching

• Transaction delay: In some cases, there may be delays in the trading system, especially during periods of high volatility, where order processing may be slower than usual. This can lead to differences between the price you see for each transaction and the actual price that can be traded.
• Matching mechanism: The matching mechanism of the stock market sometimes experiences a brief lag due to large order volume and high transaction density, which may result in not immediately matching the corresponding buy order even if your selling price is lower than the transaction price.

5.Pre-market and after-hours trading

• The impact of pre-market and after-hours trading: If you place an order during the pre-market or after-hours period, the liquidity during these periods is usually lower than that during regular trading hours, resulting in a sell price lower than the individual price but still not traded. The transaction prices during pre-market and after-hours trading may differ from those during regular trading hours.

6.Bourse matchmaking rules

• Trading rules and priorities: Different exchanges may have different matching rules, such as prioritizing market orders or orders placed at different times. These rules may cause your order to fail to be executed immediately, even if the selling price is lower than the transaction price.

7.Allocation of orders across multiple markets

• Multi-market trading: If a stock is listed on multiple exchanges, orders may be executed in different markets. Your order may not be matched with enough buy orders in one market, even though the transaction price is higher in another market.

When encountering situations where the selling price of US stocks is lower than the transaction price but cannot be executed, investors should consider various factors such as order type, market liquidity, price slippage, trading delays, and premarket and after-hours trading. Understanding these market mechanisms can help investors better cope with uncertainty in trading and adopt appropriate strategies to optimize trading results. If frequent unexecuted issues occur, it may be helpful to consider using market orders or checking whether market liquidity is sufficient.