Trading orders can be stopped or canceled for a number of reasons, including the following:

• You've reached your daily trading limit, which can vary based on the type of account and the type of assets you’re trading.
• An individual stock or crypto sometimes has buying limits because of active risk controls in place.
• A circuit breaker or market-wide trading halt
• Exchange and SEC-imposed trading halts on individual stocks

For other common reasons why an order might be canceled, see Why was my order rejected.