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An exchange rate sets the conversion value between currencies when you run a transaction. Two conversion directions are supported:
  • Fiat to stablecoin (e.g. USD to USDC).
  • Stablecoin to fiat (e.g. USDT to BRL).
Rates move with market conditions, liquidity, and the pair you’re converting.

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Exchange rate types

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Floating rate

A floating rate is a real-time reference rate without a price lock. Use it to show estimated conversion amounts in your UI. The actual rate applied at execution time may vary slightly with market conditions. No fee. Example: display an estimated conversion amount before a user confirms a transaction.

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Locked rate

A locked rate guarantees the exact conversion rate for a specific time window. When you request one, you get an exchangeRateId that locks in the quoted rate. Pass that ID on the transaction request to settle at the quoted rate. Available durations: 30s, 1m, and 5m. The 30-second lock has no fee. Longer durations include a fee to cover volatility risk. If the lock expires before the transaction is submitted, the exchangeRateId is no longer valid — request a new rate to continue. Example: quote a guaranteed price to a customer so they have time to review and confirm before the rate expires. Request a locked rate:
POST /exchange-rates
curl https://api-sandbox.lumx.io/exchange-rates \
  -X POST \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "customerId": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
    "type": "LOCKED",
    "rail": "PIX",
    "sourceCurrency": "BRL",
    "targetCurrency": "USDC",
    "sourceAmount": "59255.50",
    "timelock": "1m"
  }'
Response
{
  "id": "123e4567-e89b-12d3-a456-426614174001",
  "type": "LOCKED",
  "rail": "PIX",
  "sourceCurrency": "BRL",
  "sourceAmount": "59255.50",
  "targetCurrency": "USDC",
  "baseTargetAmount": "10000.000000",
  "baseExchangeRate": "5.9255",
  "finalTargetAmount": "9978.000000",
  "finalExchangeRate": "5.9386",
  "expiresAt": "2026-05-05T00:00:00Z"
}
Pass the returned id as exchangeRateId on the transaction request to settle at the quoted rate:
POST /transactions (excerpt)
{
  "exchangeRateId": "123e4567-e89b-12d3-a456-426614174001"
}

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Rate comparison

FeatureFloating rateLocked rate
Rate guaranteeNoYes
Lock durationN/A30s, 1m, 5m
Amount inputsSource amount onlySource or target amount
ExpirationNoYes
Additional feesNoNo for 30s, Yes for 1m+
Best forImmediate execution, low frictionGuaranteed pricing, exact quotes

Transactions

Apply exchange rates when moving funds between currencies.

Coverage

Supported currency pairs and conversion routes.