How do I cap an AI agent's spend when it pays merchants in more than one currency?

What should I check, step by step?

1. Pick one budget currency for the agent (the currency your card or wallet settles in) and write every cap in that currency's minor units. Check the decimals: USD and EUR have 2, JPY and KRW have 0, BHD, KWD, OMR, JOD and TND have 3 (ISO 4217).

2. Set the policy with set_spend_policy: currency (for example USD), per_tx_max_minor and daily_max_minor. A policy holds one currency, and authorize_spend denies any purchase in a different currency with currency_not_allowed, so mixed currencies never add up as raw numbers.
3. If the merchant prices in another currency, have the agent convert the price to the budget currency before calling authorize_spend, then add headroom for FX movement and fees (a few percent is a starting point; size it from your card statements). Put the original amount, currency and rate source in reference so the decision can be checked later.
4. Or give a foreign currency its own lane: issue a separate credential with issue_agent_credential and set_spend_policy on it in that currency (currency JPY, daily_max_minor 20000 means 20,000 yen). Use this when the agent pays in that currency often and you want a cap a person can read in local money.
5. Don't use reference rates as the price. The ECB publishes its euro reference rates for information purposes only and discourages using them for transactions. Use the rate your card network or payment provider applies, or a quote that includes it.
6. Watch for dynamic currency conversion at checkout (the merchant offers to charge in your home currency at its own rate). Tell the agent to pay in the merchant's local currency unless the converted price is what was authorized.
7. Keep the card limit in the card currency as the outer cap: Stripe Issuing spending_limits are set in the card's currency and smallest unit, and amounts in other currencies are converted to the card's currency when the limit is checked.
8. Reconcile in the budget currency: compare each allow (amount and reference) with the settled card amount. Differences come from FX, fees and later tips or adjustments, so expect small gaps and investigate big ones.

Why doesn't one spend cap number work when an AI agent pays in several currencies?

Payment APIs take amounts as integers in the currency's minor unit. Stripe's docs give 1099 for 10.99 USD and 10 for 10 JPY, and list special cases such as ISK, which ISO 4217 now gives 0 decimals but Stripe still represents as a two-decimal value. A cap copied from a USD config into a JPY or BHD config changes size by a factor of 100 or 10 without anyone noticing.

• ISO 4217 (the SIX-maintained list) gives most currencies 2 decimals, JPY and KRW 0, and BHD, IQD, JOD, KWD, LYD, OMR and TND 3. If the agent, your policy and your card don't agree on the currency and its decimals, the cap isn't the cap.
• Exchange rates add drift. The price the agent saw, the rate it used and the amount the card network settles can all differ, and Stripe notes that tips and fees can be posted later and push spend past a limit.

How do I keep an AI agent's spending policy in one budget currency?

On Rightshold, set_spend_policy stores one currency per credential next to per_tx_max_minor, daily_max_minor and the merchant allowlist. authorize_spend checks the purchase currency first: anything else is denied with currency_not_allowed, and the daily total only adds allows in the policy currency.

• That makes the conversion explicit. The agent (or your checkout code) converts to the budget currency, authorize_spend checks that amount against the caps, and the signed decision records the purchase as sent, including reference. If conversion was wrong, the record shows what was authorized and you can compare it with the card statement.
• For a currency the agent uses a lot, a separate lane credential with its own policy in that currency gives a local-currency cap (for example 20,000 JPY a day). The lanes don't share a total, so add an outer cap where the money moves.

How does a card limit in the card's currency cap an AI agent's foreign-currency spend?

Stripe Issuing spending_limits are in the card's currency, and foreign-currency authorizations are converted to that currency before the limit is checked. One card limit therefore caps all currencies together, at the network's rate, which makes it the right backstop for several Rightshold lanes.

• Rightshold does not convert currencies, quote exchange rates or move money. It checks the amount and currency it is given against the policy and signs the allow or deny. Your payment step should refuse to pay without a fresh allow (valid for 15 minutes) for the amount it is about to charge, and merchants can check it free with verify_spend_authorization.