The current Xero Payments module does not expose all aspects of the Xero Payment API. Specifically the CurrencyRate is missing, this is critical as when you are managing payments in multiple currencies and fail to include the currency exchange rate (CurrencyRate) Xero applies it's own currency rate - which is never the same. This means when your payment is recorded in Xero and your book keeping staff are reconciling the transactions the correct transaction NEVER appears because the rates and therefore the payment amounts do not match.
Without this fix the Xero Payments module is useless to international users.