Your questions about SoFi Hong Kong are answered here

If you don’t have enough settlement currency in your account to settle a trade, you are required to convert your available funds into the settlement currency through SoFi Hong Kong App or make a deposit. Otherwise, SoFi Hong Kong will conduct FX conversion to cover the deficit currencies at 11:00 HKT on the next business date after your trade is executed. Interest (P+8%) can be charged if your account has a negative cash balance in any currencies. Please see the FAQ Fees and Charges Table for details. Please note that FX conversion will be processed on business days (Monday to Friday, exclude Hong Kong public holidays) only. We would recommend you to check your SoFi Hong Kong App for the status of your balance and transactions before placing instructions to buy securities.