Introduction to One-click Checkout: Build One-click Checkout Extensions for Payment Gateways

Integrating third-party payment gateways into a custom Fynd Commerce checkout flow presents several challenges. Storefronts often need to modify the default checkout process to support features such as "Buy Now" functionality and to apply custom cart validation logic. At the same time, payment flows require highly secure, reliable backend logic to prevent fraud, verify payments, and ensure accurate order creation and tracking. Maintaining synchronization among the backend, payment gateway, and frontend is critical; any misalignment can lead to lost orders, duplicate charges, or a poor customer experience. After payment, users must be redirected to the appropriate success or failure pages, with all relevant order details available for tracking and feedback.

The variety of payment providers, each with unique SDKs, APIs, and signature verification methods, makes unified logic and thorough documentation necessary. Without addressing these complexities, merchants may face payment failures, abandoned carts, and reconciliation issues, which can negatively affect sales and customer satisfaction.

This documentation presents a comprehensive framework for building One-click checkout flows that integrate smoothly with external payment gateways. It addresses all key aspects of integration, including client-side code injection to intercept Buy Now or Checkout actions, backend endpoint design for payment initiation and verification, and secure processing of payment callback data to prevent tampering or duplicate orders.

The documentation also explains how to ensure users are consistently redirected to accurate, trackable order status pages after payment. All recommended practices and code samples are pluggable and provider-agnostic, enabling them to be adapted to various payment gateways with minimal effort. Additionally, the guide covers best practices for API security, input validation, and error handling to ensure a reliable, maintainable solution. By following this approach, you can create a secure, conversion-optimized One-click checkout solution for Fynd Commerce that supports any payment gateway integration.

Steps Overview

The checkout extension flow follows this sequence:

1. Script Injection: Inject client-side script to intercept Buy Now/Checkout actions
2. Buy Now Handler: Frontend handler intercepts AddItemsToCart mutation when buyNow: true (covered in Script Injection)
3. Buy Now Endpoint: Backend endpoint creates payment gateway order and returns popup configuration (covered in Script Injection and Controllers)
4. Payment Handler: Frontend handler processes the payment response from the payment gateway
5. Verify Endpoint: Backend endpoint verifies payment signature, fetches addresses, completes checkout, and updates payment.
6. Redirect: Frontend redirects to the success page with the order ID.

Each step is documented in detail in the following pages. Start with Getting Started to understand the implementation approaches and prerequisites, then proceed to Script Injection to begin implementing the checkout flow.

Each step builds on the previous one. The script injection creates the order, the payment handler receives the payment response, the verify endpoint processes it, and redirection completes the user journey.

Quick Start

Before diving into implementation details, make sure you:

1. Review the Getting Started Guide: Understand the different implementation approaches, framework, and in the Prerequisites section.
2. Follow the Framework: Use the Framework for consistent implementation across payment providers

For detailed information on implementation approaches, the recommended framework, and prerequisites, see the Getting Started guide.