Your questions about SoFi Hong Kong are answered here

You will need to have sufficient fiat currencies or virtual assets in your account to execute your trade.

Crypto accounts do not support direct fund deposits. Funds must be transferred from your existing Direct Invest account. You can use the following features on the Crypto portfolio page:

• Transfer: Move funds between your Direct Invest account and Crypto account.
• Cash History: View past transfer and exchange records.