Nuvei Payments API
Server-to-server REST API for processing card and APM transactions through Nuvei. Includes openOrder for session setup, payment for end-to-end transactions, settleTransaction for capturing pre-authorized amounts, refundTransaction for refunds, voidTransaction for cancellations, and getPaymentStatus for transaction state. Auth uses SHA-256 checksum over merchantId, merchantSiteId, clientRequestId, amount, currency, timeStamp, and merchantSecretKey.