At payment initiation, detect whether the merchant charges in a currency different from the agent's base currency; source this from the PSP's payment intent response or the merchant's checkout page, not assumptions.
Evaluate whether to pay in the merchant's currency (dynamic currency conversion by the card network, typically better rates) or accept a local currency conversion if the merchant offers DCC (dynamic currency conversion by the merchant — almost always worse for the buyer; decline it).
Record both the transaction currency and amount, and the base currency equivalent at the exchange rate applied; store the exchange rate source and timestamp for reconciliation.
Apply FX budget headroom: if your spend cap is denominated in base currency, calculate the equivalent cap in transaction currency using a real-time rate with a buffer (e.g., 2–5%) to account for rate movement between authorization and settlement.
At settlement, the actual base-currency debit may differ from the authorized amount due to exchange rate movement; reconcile the settled amount (from the card statement) against the authorized equivalent and record the FX difference as a separate line in your ledger.
If multi-currency spend is significant, evaluate using a card product that settles in multiple currencies natively to reduce conversion costs and simplify reconciliation.
Known gotchas
Authorization and settlement rates can differ by a meaningful margin for volatile currencies; a charge authorized at one rate that settles two days later at a worse rate can cause a budget overrun even when the authorization was within policy — build settlement-rate variance into your budget model.
DCC (dynamic currency conversion) offered at point of sale or at checkout is almost always more expensive than letting the card network convert; train the agent to detect and reject DCC offers, which often appear as a checkbox or pre-selected radio button.
Reporting in base currency when transactions occur in multiple currencies requires a consistent FX rate methodology (spot rate at transaction date, average monthly rate, etc.); choose one and apply it consistently or your reports will be non-comparable across periods.
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