In case you decide to use a different currency in the invoice compared to what your default currency is, CSP will ask you to input the exchange rate between those currencies.
For example: If you are a UK supplier, your default currency is GBP. If the PO you invoice against is in EUR, CSP will ask you to input the exchange rate from EUR to GBP.
Please know that the currency of the invoice should match the currency of the PO.