Why was my Cash Quantity order for a fractional share rejected?

TWS provides a built-in, dynamic method to transact stock orders using a specified cash value instead of a share quantity. Cash Quantity allows the user to enter a cash amount in the Quantity field, which is then used along with the bid/ask price to drive the number of shares purchased With Cash Quantity, the entered cash value remains constant and the share size varies based on fill price…

While mutual fund opening orders can only be entered in whole dollar amounts, any sell order including closing orders must be entered in share units. In the case of fractional shares, closing orders may be entered in the fractional share quantity…

Generally when you buy a stock, you specify the order size using a share amount. With the Cash Quantity feature, you can specify the size of the buy order using a cash amount instead of the number of shares. When you use Cash Quantity for the order size, the cash value drives the number of shares. If the share price moves, the number of shares is adjusted to accommodate the entered cash amount…

Generally when you buy a stock, you specify the order size using a share amount. With the Cash Quantity feature, you can specify the size of the buy order using a cash amount instead of the number of shares. When you use Cash Quantity for the order size, the cash value drives the number of shares. If the share price moves, the number of shares is adjusted to accommodate the entered cash amount…