When I authorise a payment, what funding sources will be used to capture the funds?

When the merchant captures the authorisation, the currency in which the item is priced is used first. If this currency is not sufficient, your primary balance will be used to fund the transaction. The exchange rate used to convert your balances to the seller's designated currency is whatever the exchange rate is at the time the funds are captured.

If there are insufficient funds in your two balances to complete a payment, PayPal will capture the remainder of the funds to complete the payment from the backup funding source you designated during the authorisation.