API Integration Patterns for eCommerce

A modern eCommerce operation involves multiple systems: your store platform, accounting software, inventory management, shipping carriers, email marketing, analytics, and perhaps more. When these systems don't communicate, staff spend hours on manual data entry, and errors creep in from re-keying information.

API integrations solve this by allowing systems to exchange data automatically. Orders flow from your store to your accounting software without human intervention. Inventory updates sync across channels. Customer data populates your marketing tools in real-time.

This article explores common integration patterns for eCommerce and practical considerations for implementing them well.

Understanding APIs

An API (Application Programming Interface) is a structured way for software systems to communicate. Rather than exporting CSV files and importing them elsewhere, APIs allow systems to request and send data programmatically.

Most modern business software exposes APIs. Your accounting software likely has one. Your eCommerce platform certainly does. Shipping carriers, payment processors, email tools—all accessible through APIs.

The challenge isn't whether integration is possible, but how to implement it well: handling errors gracefully, managing data consistency, and building systems that remain reliable as your business scales.

Common Integration Points

Accounting Systems

Perhaps the most valuable integration for many stores. When an order is placed, the invoice automatically appears in Xero, QuickBooks, or Sage. When payment clears, it's recorded. When a refund is issued, accounting reflects it.

This eliminates manual invoice creation and ensures your books accurately reflect transactions. End-of-month reconciliation goes from hours to minutes.

Key considerations:

• Tax handling—VAT rates must map correctly between systems
• Payment methods—different payment types may need different treatment
• Refunds and partial refunds—these must reverse the original correctly
• Currency—multi-currency stores need careful handling

Inventory Management

Accurate stock levels prevent overselling and missed sales. When you sell across multiple channels—website, marketplaces, physical stores—inventory integration becomes essential.

A sale on your website should immediately reduce available stock on Amazon and eBay. A shipment received in your warehouse should update availability everywhere simultaneously. Without integration, you're racing against time with spreadsheets.

Inventory integration patterns:

• Central inventory as source of truth, pushing to all channels
• Event-driven updates—changes trigger immediate syncs
• Periodic full syncs as a safety net for any missed events
• Buffer stock—reserving inventory to prevent overselling during sync delays

Shipping and Fulfilment

Shipping integrations streamline order dispatch. Instead of manually entering shipment details into carrier systems, orders flow automatically. Labels print, tracking numbers return, and customers receive shipping notifications.

For multi-carrier setups, integration enables intelligent carrier selection—the cheapest option for standard delivery, the fastest for express, the most suitable for oversized items—all decided automatically.

Common integrations include Royal Mail, DPD, DHL, UPS, FedEx, and aggregators like ShipStation or Shippo that provide unified APIs across carriers.

Marketing Platforms

Customer and order data powers marketing automation. Email platforms like Mailchimp, Klaviyo, or Brevo can segment customers based on purchase behaviour, trigger abandoned cart sequences, and send personalised recommendations.

Integration ensures:

• Customer lists stay current automatically
• Purchase history informs segmentation
• Transactional emails (order confirmations, shipping updates) can be managed alongside marketing
• Revenue attribution tracks which campaigns drive sales

Customer Service Tools

Support teams need order information to help customers. Integrating your store with helpdesk software (Zendesk, Freshdesk, Help Scout) provides agents with order history, shipping status, and customer details within their support interface.

This speeds resolution and improves customer experience. Agents don't ask customers to repeat order numbers or switch between multiple systems to find information.

Integration Approaches

Direct Integration

Your store communicates directly with each external system. You build (or commission) custom code that connects your specific platforms.

Advantages:

• Full control over behaviour and data mapping
• No ongoing subscription costs beyond hosting
• Can handle complex, unique requirements

Disadvantages:

• Higher upfront development cost
• Maintenance required when APIs change
• Each new integration requires custom work

Integration Platforms

Services like Zapier, Make (formerly Integromat), or n8n provide pre-built connectors between common platforms. You configure workflows through visual interfaces rather than writing code.

Advantages:

• Faster to set up for common integrations
• No development skills required
• Connectors maintained by the platform

Disadvantages:

• Ongoing subscription costs
• Limited flexibility for complex logic
• Can become expensive at high volumes
• Dependency on third-party service

Middleware

A custom integration layer sits between your store and other systems. This middleware receives events from your store, transforms data as needed, and distributes to connected systems.

This is the approach we typically recommend for businesses with multiple integrations or complex requirements. FeathersJS works excellently for this purpose.

Advantages:

• Centralised integration logic
• Consistent error handling and logging
• Easy to add new integrations
• Full control over business rules

Disadvantages:

• Higher initial investment than integration platforms
• Requires hosting and maintenance

Building Reliable Integrations

Integrations that work in testing can fail in production. Building reliability requires anticipating and handling failure modes:

Handle API Failures

External APIs go down, return errors, or time out. Your integration should:

• Retry failed requests with exponential backoff
• Queue operations when external systems are unavailable
• Alert you to persistent failures
• Not lose data even when external systems are down

Manage Rate Limits

Most APIs limit how many requests you can make. Hitting limits causes requests to fail. Design integrations to stay within limits, queue excess requests, and handle rate-limit errors gracefully.

Ensure Data Consistency

When data exists in multiple systems, consistency matters. If an order appears in your store but not your accounting software, something's wrong. Build mechanisms to detect and resolve inconsistencies.

Log Everything

When something goes wrong (it will), you need to understand what happened. Comprehensive logging of requests, responses, and errors makes debugging possible.

Monitor Actively

Don't wait for customers to report problems. Monitor integration health—are syncs completing? Are error rates increasing? Are queues backing up? Catch issues before they impact customers.

Planning Your Integration Strategy

If you're considering integrating your eCommerce systems, start with these questions:

• Which manual processes consume the most time or cause the most errors?
• What data needs to flow between systems, and in which direction?
• How quickly must updates sync? Real-time, hourly, daily?
• What's the cost of integration failure—inconvenience or business-critical?
• Do you have technical resources for custom development, or need low-code solutions?

For straightforward needs with common platforms, integration tools like Zapier may be sufficient. For complex requirements, multiple integrations, or high volumes, custom development often provides better long-term value.

We regularly help eCommerce businesses design and implement integration strategies. Get in touch to discuss your specific requirements and we'll recommend an appropriate approach.