This forum is to discuss different features/issues of Oracle Financials modules ( GL - General Ledger, AP - Accounts Payable, AR - Accounts Receivable, FA - Fixed Assets & CM - Cash Management ).
An invoice has to be paid in the currency which it has been recorded. The exception exists for EURO derived currencies where a fixed conversion factor exists between european currencies.
You can not change the payment currency in the invoice unless it is EUR related currencies. However, you can make payment from VND bank account (or USD bank account) if VND is the functional currency.