visa vcf file which field should I load for transaction amount

We are using visa vcf file to load transaction into internet expenses.  there are posted amount field and billed_amount field.  but there are no value for the transaction_amount field.  Our currency is USD only hence all records are loaded as USD.  Once in a while we will have some Canadian travel charges.  The amount is different between posted_amount is in Canadian dollar and billed_amount is in USD.  When the amount is not equal, we get a error message " receipt currency is the same as the reimbursement currency, the exchange rate will default to 1' hence could not create the