There are two main reasons for negative balance to appear in your account. First, when placing a market order, the actual amount needed to purchase your order might be higher than the indicative price shown on the app, hence the potential negative balance.

Another possible reason is that if a trade is placed from a different currency, e.g. buying US stocks with HKD balances, the difference in the currency exchange rates between the time of order placement vs fund conversion (normally on the next business day) will result in a negative balance.

You are advised to settle the negative balance as soon as possible, before we forced settle the amount. Interest may be incurred.