Checkout API

Overview

A checkout API lets an application create and manage the payment session, amounts, currencies, customer context, and status behind a checkout experience. A checkout API provides server-side operations for initiating and tracking a customer payment flow. Client-supplied prices, return-page parameters, or browser success messages must not determine fulfillment. Testing Checkout API should cover malformed input, denied access, rate limits, timeouts, duplicates, asynchronous completion, and version changes.

The API request should use an idempotency key and an authoritative server-calculated amount. Final status usually arrives through a signed webhook or a verified status request. Integrators should define cancellation, expiration, underpayment, overpayment, confirmation, refund, and duplicate-customer behavior. Sandbox coverage should include failures and delayed blockchain confirmations, not only the happy path. The Checkout API contract should define identifiers, validation, authorization, status semantics, errors, limits, and version behavior at the same boundary.

For Checkout API, metrics should separate transport success from business success. It may create a hosted payment page, return a session identifier or URL, define accepted currencies, specify expiration, and associate the payment with an internal order. URLs must be validated, secrets kept server-side, and order references preserved through reconciliation. Changes to Checkout API should be checked against older clients, stored payloads, enum growth, default behavior, and retry assumptions.

The Checkout API owner should publish stable error semantics and guidance on whether correction, retry, status lookup, or escalation is appropriate.

Data handled by Checkout API should use documented types, units, timestamp rules, nullable fields, and enum behavior to prevent silent interpretation errors.