To account for any last-minute price fluctuations of securities, foreign exchange changes, and Syfe fees, we keep a very small amount of buying power as a buffer while placing orders to exchanges which is released as soon as the order is placed. This is to avoid any order cancellation because of insufficient balances.

Please note that your buying power amount will be different for each market as it is based on the currency the asset is traded in. For more information, please refer to this article.