Ecommerce Integration Explained: Connectors, Middleware and Custom APIs

For most stores, the storefront is one system among several. Prices and stock come from an ERP, product content from a PIM, shipments from a warehouse or 3PL, tax from a tax engine, and orders may also arrive from marketplaces or a trading partner's EDI feed. Ecommerce integration is the work of connecting those systems so data moves between them on schedule, without rekeying, and with one clear owner for every record. For B2B merchants the ERP is usually the connection that matters most, and it is where our ERP integration services start.

This guide covers the ecommerce integrations a typical store needs, the five patterns used to build them (app connectors, iPaaS middleware, custom API integrations, scheduled files and EDI), how to choose between them, and how to keep integrations from failing quietly. The examples come from integrations we have built on Magento and Adobe Commerce, and the same principles apply on Shopify and BigCommerce.

The ecommerce integrations a store usually needs

Start with an inventory of systems, not a list of features. Most stores connect to some combination of these:

System	What it usually owns	Typical flows with the store
ERP	Customers, pricing, inventory, orders, invoices	Prices and stock in, orders out, shipments and invoices back
PIM	Product content, attributes, images	Products and attributes in
OMS, WMS or 3PL	Allocation, picking, packing, shipping	Orders out, shipments and tracking in
CRM	Contacts, accounts, sales activity	Customers and orders out, account owners in
Tax engine	Tax rates, exemptions	Cart and address out, tax amount back at checkout
Payment gateway	Authorization, capture, refunds	Live calls at checkout, capture and refunds later
Marketplaces	Listings and orders on channels such as Amazon	Products and stock out, orders in
Supplier and distributor feeds	Vendor stock and cost	Stock and cost in, dropship orders out

A small brand may need only tax, payments and a 3PL. A distributor may need all eight, with the ERP in the middle. Count flows as well as systems: an ERP connection that moves prices, stock, customers, orders, shipments and invoices is six integrations to design, test and monitor.

Five ecommerce integration patterns

App connectors

A connector is a pre-built app, sold through the platform's marketplace or by the other system's vendor, that maps the common objects between two systems. You configure mappings and a schedule, and the vendor maintains the code. Connectors are the fastest way to launch when your processes are close to the defaults. Their limits show up in custom fields, unusual pricing rules and errors you cannot see into.

Warner Press, a publisher of church, ministry and education resources, syncs customer and order data between its Magento store and Sage Intacct through the Greytrix GUMU connector. Our work there validated the connector's transfers, error handling and sync timing, then extended the store's Payfabric payment module and Order API so full transaction detail reaches Sage Intacct and payments reconcile there. The connector handles the standard objects, and custom code covers the gaps.

iPaaS and middleware

An integration platform as a service, such as Celigo, Boomi or MuleSoft, sits between your systems and handles mapping, transformation, queuing, retries and dashboards. Instead of a web of point-to-point connections, every system talks to the hub. iPaaS suits companies that integrate many systems and have someone to own the platform. The costs are a subscription and the platform's way of modeling flows, which deeply custom logic can end up fighting.

On the Adobe Commerce Cloud platform we are building for Inyo Pools, a pool and spa parts retailer, we are building the Sage 100 integration over cloud middleware in both directions: inventory, product cost, orders, shipments, invoicing and returns, with Sage as the financial source of truth. Our Sage 100 ecommerce integration page covers that ERP in more depth.

Custom API integrations

A custom ecommerce API integration is code written directly against both systems' interfaces: the store's REST or GraphQL APIs on one side, and the ERP's REST, SOAP or OData services on the other. You get full control and no extra license. You also own every line, including retries, logging and upgrades.

DMC, a manufacturer of aerospace and defense tooling, runs its Adobe Commerce B2B store on a bidirectional integration with Infor SyteLine through SyteLine's IDO REST API. It carries customers, addresses, payment terms, products, inventory, lead times, orders and shipments, writes a due date back to SyteLine for each order line, and triggers card capture after shipment. The original specification called for Celigo, but flows that tightly coupled to the ERP did not fit a generic middleware layer, so we built the integration directly.

Inyo Pools shows the other common reason to go custom: no connector exists. Each of the three distributor integrations we are building speaks a different dialect (token-based REST, XML over HTTPS across more than 16 warehouses, and REST that carries tracking inside invoice payloads), and each is normalized into one inventory and cost model.

Scheduled file exchange

Files on a schedule, usually CSV or XML over SFTP, are the oldest pattern and still a valid one. They suit large ERPs with established batch jobs and IT teams that prefer not to open the ERP to direct API calls. On the Magento store of a Fortune 500 equipment manufacturer we worked with, order and inventory data moved as scheduled, SAP-ready files over SFTP. The risks are latency, partial or duplicate files, and errors that surface hours later, so file integrations need naming rules, row counts and an archive of processed files.

EDI

Electronic data interchange is the standard language of retail, distribution and manufacturing supply chains. In North America that usually means ANSI X12 documents such as the 850 purchase order, 855 acknowledgment, 856 advance ship notice and 810 invoice, sent over AS2, SFTP or a value-added network. If your back office or your largest customers already run on EDI, the store can join that flow instead of creating a new one. ADTRAN, a networking and broadband equipment manufacturer, pushes each order from its Adobe Commerce B2B store into its back-office ERP via EDI in real time, so the operations team no longer re-keys orders customers already entered.

Ecommerce platform integration: what each platform offers

The platform decides which tools you start with.

• Magento Open Source and Adobe Commerce expose REST and GraphQL APIs plus asynchronous and bulk REST endpoints for large jobs. Adobe Commerce adds Adobe I/O Events, webhooks, App Builder and API Mesh for integrations that run outside the application. See our Magento ERP integration and Adobe Commerce integrations pages.
• Shopify now treats its REST Admin API as legacy, so new integrations should use the GraphQL Admin API, webhooks and bulk operations, within Shopify's rate limits. Our Shopify integration services cover custom apps and ERP connections.
• BigCommerce offers REST management APIs, a GraphQL Storefront API and webhooks.

Data ownership and mapping

Integration problems usually start with ownership, not technology. Two systems that both believe they own the same customer, price or stock level will overwrite each other sooner or later. Before anyone writes code, name one system of record for every object and every disputed field, and decide which direction each flow runs.

Then map the data. The fields that cause trouble are rarely the obvious ones:

• Identifiers. Customer numbers, SKUs and order numbers must match exactly. At DMC, years of inconsistent data entry had produced short account numbers such as A252 alongside the canonical A000252, which caused silent matching failures until we normalized them across the customer base.
• Vendor part numbers. When several suppliers sell the same item, a mapping layer has to tie each catalog SKU to each supplier's part number, as it does for Inyo Pools.
• Units of measure. The store sells by the each while the ERP stocks by the case, or the reverse.
• Statuses and codes. Order statuses, shipping methods, payment terms and tax codes rarely share names across systems.
• Custom fields. A new field is only useful if downstream systems can read it. For Warner Press we extended the Magento Order and Customer REST APIs so the ERP receives every custom field added to the store.

Error handling and monitoring

Integrations fail quietly. A good one assumes failure and makes it visible.

• Make writes idempotent. Key each write on the order number or another business key so a retry never creates a duplicate order.
• Retry transient errors and park permanent ones. A timeout deserves a retry with backoff. A missing SKU does not, so it goes to an error queue with the payload and the reason.
• Alert the person who can fix it. A bad SKU goes to merchandising, a credit hold to finance.
• Reconcile on a schedule. Compare daily order counts and totals between the store and the ERP, and sample stock levels. Reconciliation catches what alerts miss.
• Plan for downtime. Decide what the store does when the ERP is unavailable: queue orders, fall back to the last synced prices and stock, or hold checkout.
• Log with business keys. Support should be able to trace one order across every system by its number.

Choosing ecommerce integration solutions: a decision table

Pattern	Best fit	Watch out for	Example from our work
App connector	Standard flows between two systems, processes close to defaults	Mapping limits, hidden errors, one connector per system pair	Warner Press: Magento to Sage Intacct through Greytrix GUMU
iPaaS or middleware	Many systems, an owner for the platform, a need for queues and dashboards	Subscription cost, custom logic that fights the tool	Inyo Pools: Sage 100 over cloud middleware (in progress)
Custom API	Logic specific to your business, real-time needs, no connector available	You own maintenance, monitoring and upgrades	DMC: Infor SyteLine through the IDO REST API
Scheduled files	Large ERPs with batch jobs, volumes that tolerate delay	Latency, partial files, duplicate processing	A Fortune 500 equipment manufacturer: SAP-ready files over SFTP
EDI	Back offices and trading partners that already use EDI	Translator and mapping costs, partner-specific variations	ADTRAN: real-time EDI order push to the ERP

Most mature stacks mix patterns. Warner Press pairs a connector with custom API extensions, and Inyo Pools combines custom distributor integrations with middleware for Sage 100. A useful rule: buy the commodity flows, such as orders out and tracking in, and build only the flows that encode how your business is different, usually pricing, account structure and fulfillment rules.

A pre-project checklist

1. List every system, with its edition and version.
2. Name the system of record for each object and each disputed field.
3. Set the direction and freshness of each flow: live, every few minutes, hourly or nightly.
4. Pull sample data and map identifiers, units of measure, statuses, shipping methods and tax codes.
5. Document the APIs or file formats each system exposes, with authentication and rate limits.
6. Define failure handling: retries, error queues, alerts and who receives them.
7. Decide what the store does when each connected system is down.
8. Decide which history moves at launch, such as open orders, customers and invoices.
9. Write test cases for the edge cases: partial shipments, backorders, credit holds, returns and canceled lines.
10. Name an owner for each integration after launch.

When to bring in ecommerce integration services

With one or two systems and standard processes, a well-configured connector may be all you need. Outside help earns its cost when the ERP holds contract pricing or account hierarchies, or when no connector fits. Our ERP-specific pages cover NetSuite integration services and Microsoft Dynamics ecommerce integration, and our guide to connecting Magento with SAP, NetSuite and Dynamics goes deeper on those three ERPs.

Frequently asked questions

What is ecommerce integration?

Ecommerce integration connects an online store to the other systems a business runs on, such as an ERP, PIM, warehouse or 3PL, CRM, tax engine, payment gateway and marketplaces. It moves products, prices, inventory, customers, orders and shipments between them automatically, so staff do not rekey data and every system agrees.

What is the difference between a connector and iPaaS?

A connector is a pre-built app that links two specific systems with standard mappings. An iPaaS such as Celigo, Boomi or MuleSoft is a platform for building and running many integrations in one place, with its own mapping tools, queues and monitoring. Connectors are faster to launch, and iPaaS scales better when many systems share data.

Is EDI still used in ecommerce?

Yes. EDI remains the standard for purchase orders, ship notices and invoices between manufacturers, distributors and large retailers. A store can feed orders into an EDI flow the back office already runs.

Should every integration run in real time?

No. Checkout tax, payment authorization and sometimes customer-specific pricing need live calls. Inventory, order export and shipment updates usually work well on short schedules. Every live call makes the store depend on the other system being up, so use them only where accuracy at that moment matters.