Generally, Futu Niu Niu uses mainland cards to purchase foreign exchange through banks for cross-border remittance. It should be noted that investors can't transfer their funds to the mainland when trading Hong Kong stocks with mainland cards on Futu Niu Niu. Investors need to re-open a Hong Kong bank card or an overseas card. After selling Hong Kong stocks, you can first transfer the funds to Hong Kong bank cards or overseas cards, and then transfer them from Hong Kong bank cards or overseas cards to mainland bank cards.