Complex Position Size
For complex, multi-leg options positions comprising two or more legs, TWS might not track all changes to this position, e.g. a vertical spread where the short leg is assigned and the user re-writes the same leg the next day, or if the user creates a the position over multiple trades, or if the order is not filled as a native combination at the exchange.
If you received a message because you are submitting an order to close a position, roll a position, or modify a position using the “% Change” feature, it means that the maximum quantity of option positions in your account that are available to close for this order is different from that of the original position tracked by TWS.
Before submitting, you should review the order and confirm that the order quantity we have calculated is the correct quantity that you want to trade.