SetHoldings: Invalid Quantity

The error message you're seeing is due to insufficient buying power. The SetHoldings method uses market order to reach the target portfolio weight you provide. If the portfolio weight you provide translates to an order quantity that exceeds your buying power, you will encounter an InsufficientBuyingPower error.

In your case, you're trying to allocate 100% of your portfolio to QQQ. However, due to price fluctuations and transaction fees, the total cost of the order may exceed your available balance.

To avoid this, you can adjust your buying power buffer or ensure you have enough margin remaining to cover the initial margin requirements of the order before placing it. You can also check if the quantity of the order is non-zero before you place the order.

Here's how you can adjust your buying power buffer in Python:

self.Settings.FreePortfolioValuePercentage = 0.05

This sets aside 5% of your portfolio value as a buffer.

For more information, you can refer to the following documentation:

• Order Errors
• Buying Power
• Position Sizing

But commissions at IB are minimal and QQQ's price fluctuations are small. $10708.06 / 27 = $396. At no point today or in recent days has QQQ reached $390. How does 27 shares of QQQ translate to $10708.06?

The calculation you're making seems correct, and it's indeed strange that the total cost of the order is significantly higher than expected. However, the error message you're seeing is from Interactive Brokers, not QuantConnect. It's possible that there might be some additional fees or margin requirements that are not immediately apparent.

One thing to note is that the cost of an order in a live trading environment can be influenced by several factors, including but not limited to:

• The spread between the bid and ask prices
• The impact of market orders on the market price
• Slippage
• Brokerage fees and commissions

While the commission for US equities on Interactive Brokers is indeed minimal ($0.005/share with a $1 minimum fee and a 0.5% maximum fee), other factors could potentially increase the cost of the order.

If you're certain that none of these factors account for the discrepancy, I would recommend reaching out to Interactive Brokers' support for clarification on the error message. They should be able to provide a detailed breakdown of the costs associated with the order.

For more information on transaction fees, you can refer to the QuantConnect documentation.