Payment APIs
Payment APIs are the developer interfaces that connect applications to payment infrastructure. They abstract the complexity of bank networks, card schemes, and compliance into clean REST endpoints and SDKs — letting developers build payment flows, subscriptions, payouts, and refunds in hours rather than months.
A payment API is a REST or GraphQL interface provided by payment gateways that allows developers to programmatically initiate charges, create subscriptions, issue refunds, handle webhooks, and manage payment flows without a GUI. For international projects: Stripe has the best developer experience with the most comprehensive documentation, SDKs in every major language, and a consistent API design. For Indian projects: Razorpay API provides full UPI support, strong documentation, and a fast-growing SDK ecosystem. Both offer sandbox/test environments for development.
Key takeaways
- Stripe's Payment Intents API is the industry standard for modern payment flows — it handles 3DS2/SCA authentication, multi-step flows, and is required for European compliance.
- Always use server-side API calls for sensitive operations (creating charges, retrieving secrets). Never expose your secret API key to client-side code.
- Webhooks are critical — do not rely solely on client-side redirects to confirm payment success. Always verify payment status via webhook or server-side API call.
- Validate all webhook signatures using the gateway's secret to prevent spoofed events from triggering fulfillment.
- Razorpay's Orders API is the recommended flow for Indian integrations — create an order on the server, capture signature verification after payment.
- Test with realistic scenarios in sandbox mode: declined cards, 3DS2 challenges, webhooks, subscription renewals, and refunds before going live.
Payment API comparison
| API | Key features | Languages |
|---|---|---|
| Stripe API | Payment Intents, Connect, Billing, Radar | Node/Python/Ruby/Go/Java/.NET |
| Razorpay API | Orders, UPI, Subscriptions, Payouts | Node/Python/PHP/Java/Go |
| Cashfree API | Payment Gateway, Payouts, AutoCollect | Node/Python/PHP/Java |
| Adyen API | CheckoutAPI, Recurring, Payouts | All major languages |
| PayPal API | Orders, Subscriptions, Payouts | Node/Python/PHP/Java |
| Braintree API | GraphQL + REST, Tokenization | Node/Ruby/Python/PHP/Java |
Payment API integration checklist
- Create test and production API key pairs — never hardcode them in source code
- Install official SDK for your language (npm install stripe / razorpay)
- Create payment orders/intents server-side using your secret key
- Render payment UI using client-side SDK (Stripe.js / Razorpay Checkout)
- Implement webhook endpoint to receive async payment events
- Verify webhook signatures on every incoming request
- Handle idempotency keys to prevent duplicate charges on retries
- Test with all payment method types in sandbox mode
- Implement proper error handling for declined payments
- Log all payment events for debugging and reconciliation
API terminology
- REST API: HTTP-based interface with JSON responses
- Webhook: Async HTTP callback for payment events
- API Key: Authentication credential for API calls
- Idempotency: Deduplication of retried requests
- Payment Intent: Stripe's payment object with state
- Order API: Razorpay's pre-payment object
- SDK: Language-specific client library
Frequently asked questions
A payment API (Application Programming Interface) is a set of protocols and endpoints that allow software applications to communicate with payment gateways and processors. Using a payment API, developers can programmatically create payment intents, charge customers, issue refunds, create subscriptions, retrieve transaction history, and handle webhooks — all without a manual dashboard.
Stripe is widely regarded as the best payment API for developers due to its comprehensive documentation, SDKs in every major language (Python, Node.js, Ruby, PHP, Go, Java, .NET), consistent REST API design, and excellent developer experience. For Indian developers, Razorpay offers a strong API with full UPI support, clear documentation, and active developer community.
A payment webhook is an HTTP callback that a payment gateway sends to your server when a payment event occurs — such as payment.authorized, payment.captured, subscription.charged, or refund.created. Instead of polling the API for payment status, webhooks push real-time event data to your endpoint. You must verify webhook signatures to prevent spoofed events.
Payment API integration steps: (1) Create an account and get API keys (test and production). (2) Install the official SDK for your language. (3) Create a payment intent/order on your server using the secret key. (4) Use the client-side SDK to render the payment form. (5) Handle the webhook events for payment success/failure. (6) Test in sandbox mode before going live. Most gateways have step-by-step integration guides for all major frameworks.
Stripe Payment Intents is the modern API that supports Strong Customer Authentication (SCA/3DS2) required by PSD2 in Europe and handles multi-step payment flows including card authentication. The older Charges API is a simpler, single-step charge that doesn't support SCA. Stripe recommends all new integrations use Payment Intents for global compliance and higher authorization rates.
For Indian payment API integrations: Razorpay API (best for UPI + full Indian payment stack), Cashfree API (fast settlements + strong payout API), PayU API (wide acceptance, strong SMB base), and Instamojo API (best for small businesses and creators). For international payments from India: Stripe or Airwallex. All support REST APIs with JSON responses, webhooks, and multi-language SDKs.