E-Commerce Integration: Connect Your Store to ERP, WMS & Fulfillment

We build a custom middleware layer that connects Shopify's Admin API (REST or GraphQL, depending on the data type) to your ERP's API, database, or file import system. The integration registers Shopify webhooks for order creation, order updates, fulfillment events, product changes, and inventory adjustments. When a customer places an order on Shopify, the webhook fires to our middleware, which transforms the Shopify order payload into your ERP's expected format — mapping Shopify variant SKUs to your internal item numbers, resolving the customer account from email or account tags, applying the correct pricing schedule, and calculating tax based on your ERP's tax engine or an integrated service like Avalara. The transformed order posts to your ERP via API call, direct database insert, or file drop depending on what your ERP supports. For Shopify Plus merchants, we use the GraphQL Admin API for bulk operations (catalog sync, inventory updates, price changes) because it handles higher volumes without hitting rate limits — Shopify's REST API caps at 40 requests per second for Plus stores, while GraphQL uses a cost-based throttling model that allows significantly more data throughput. Inventory flows in the opposite direction: when your ERP processes a receipt, shipment, or adjustment, our middleware picks up the change (via API polling, database trigger, or webhook if your ERP supports it) and pushes the updated quantity to Shopify's Inventory API. For ERPs without APIs — older versions of Epicor, Sage 100, or AS/400-based systems — we build database-level connectors that query change tables or use timestamp-based polling to detect new and modified records. The entire pipeline includes retry logic, dead letter queuing for failed transactions, real-time monitoring dashboards, and alerting for any sync failures. Typical Shopify-to-ERP integration projects run 4–8 weeks for standard configurations and 8–12 weeks when legacy ERP systems or complex B2B pricing rules are involved.

Yes, and this is where FreedomDev does its best work. Roughly 40% of our e-commerce integration projects involve at least one legacy system that has no modern API — think AS/400, IBM iSeries, Progress OpenEdge, FoxPro, older versions of Epicor or MAPICS, or custom-built ERP systems written in COBOL, RPG, or Delphi 15–25 years ago. These systems are still running because they work — they handle order processing, inventory management, and accounting for companies doing $10M–$200M in revenue — but they were built before REST APIs existed. We connect them using four approaches, selected based on what the legacy system exposes. First, database-level integration: if we can get read/write access to the underlying database (SQL Server, DB2, Oracle, Progress), we build change data capture pipelines that detect inserts, updates, and deletes in real time using triggers, timestamp polling, or transaction log reading. This is the most reliable method and works for about 70% of legacy systems. Second, file-based integration: many older ERPs can export and import flat files — CSVs, fixed-width text files, EDI documents, or XML. We build automated pipelines that monitor export directories, parse incoming files, transform the data, and load it into your e-commerce platform's API. This works well for batch processes like nightly catalog sync or daily pricing updates. Third, screen scraping and RPA: for terminal-based or green-screen systems where database access is restricted, we build automated agents that navigate the user interface programmatically — entering data, reading screens, and extracting information exactly as a human operator would, but at machine speed. Fourth, custom wrapper APIs: we build a modern REST API that sits in front of your legacy system, translating standard HTTP requests into whatever protocol the old system understands (direct database calls, file drops, terminal commands). This gives your legacy system a modern interface that any e-commerce platform can connect to. The wrapper API approach is particularly valuable because it future-proofs the integration — when you eventually replace the legacy system, you update the wrapper's backend without changing any of the e-commerce integrations that depend on it. Legacy integration projects typically cost $15,000–$40,000 per system and take 6–12 weeks depending on complexity and documentation availability.

Real-time inventory sync requires solving three problems: detecting changes in the source system, transforming and transmitting the data, and handling conflicts when multiple systems modify inventory simultaneously. For the detection layer, the approach depends on your ERP. Modern ERPs with webhook or event support (NetSuite SuiteScript, Dynamics 365 Business Events, SAP Business One DI Events) push inventory changes to our middleware the moment they occur. For ERPs without event systems, we implement high-frequency polling — querying the ERP's inventory tables every 15–60 seconds for records with modified timestamps newer than our last poll. For legacy systems, we use database triggers that write changes to a staging table our middleware monitors. The transformation layer calculates available-to-promise (ATP) quantities, which is the number that actually matters for e-commerce. Raw on-hand quantity is misleading — it does not account for inventory already allocated to open orders, stock reserved for production, pending purchase orders that will replenish soon, or safety stock minimums that should never be sold. Our middleware applies your specific ATP formula: on-hand minus allocated minus safety stock plus pending receipts within a configurable lead time window. This ATP number is what gets pushed to your storefront. For multi-warehouse operations, we calculate ATP per location and optionally aggregate to a single storefront number or show per-warehouse availability for customers selecting pickup locations. The conflict resolution layer handles the race condition where a customer adds an item to their cart while the last unit is being sold elsewhere. We implement inventory reservation at the cart or checkout stage — decrementing available quantity when a customer starts checkout and releasing it if the cart is abandoned after a configurable timeout (typically 10–15 minutes). For high-velocity SKUs, we implement oversell thresholds that automatically hide products from the storefront when inventory drops below a configurable buffer. Sync latency from ERP change to storefront update is typically 3–10 seconds for webhook-based systems and 15–60 seconds for polling-based systems. We monitor sync lag continuously and alert if latency exceeds defined thresholds.

B2B e-commerce integration connects your storefront to your ERP and CRM in ways that support business-to-business selling workflows — which are fundamentally different from consumer e-commerce. The core difference is that B2B customers are not anonymous shoppers paying list price with a credit card. They are established accounts with negotiated pricing, payment terms, credit limits, order minimums, restricted catalogs, and multi-user purchasing hierarchies. None of the major e-commerce platforms handle this natively without significant customization or integration. Customer-specific pricing is the foundation. Your ERP stores contract pricing for each account — negotiated discounts, volume break schedules, promotional pricing, and cost-plus formulas. Our integration pulls this pricing in real time and surfaces it on the storefront per-login, so when a buyer from Account A logs in, they see their contracted $14.50/unit price, while Account B sees their negotiated $16.20/unit for the same SKU. This eliminates the manual quoting cycle and lets B2B customers self-serve orders at their correct pricing 24/7. Catalog restrictions control which products each account can see and order. A manufacturer selling to both distributors and end-users may show different product lines, restrict certain SKUs to specific customer tiers, or hide products that require special licensing. Our integration syncs customer group assignments from the ERP to the storefront's access control layer. Payment terms integration allows B2B customers to order on net-30, net-60, or custom payment terms managed in your ERP's accounts receivable module — not just credit card checkout. The storefront checks the customer's credit limit and outstanding balance before accepting an order and creates an AR invoice in the ERP instead of processing a card payment. Order approval workflows allow B2B accounts to set up purchasing hierarchies where junior buyers submit orders that require manager approval before they process. Multi-address shipping supports B2B accounts with multiple ship-to locations, each with their own tax settings and carrier preferences. Reorder and quick-order functionality lets buyers repeat previous orders or paste item numbers and quantities from their own purchasing systems. All of this data lives in your ERP and CRM — the storefront is just the interface. Our integration keeps both sides in sync so your sales team manages accounts in the ERP while customers self-serve through the storefront.

Cost depends on four variables: the e-commerce platform, the backend systems being connected, the number of data flows (orders, inventory, pricing, fulfillment, payments), and whether legacy systems are involved. A straightforward Shopify-to-modern-ERP integration covering bi-directional order sync and real-time inventory typically runs $15,000–$30,000 and takes 4–6 weeks. This covers discovery, data mapping, development, testing, parallel validation, and cutover. Adding pricing sync, catalog management, and fulfillment integration brings the total to $30,000–$60,000. Complex B2B integrations with customer-specific pricing, payment terms, catalog restrictions, and multi-warehouse ATP calculations typically run $60,000–$120,000. Enterprise projects connecting multiple storefronts (B2B and B2C) to ERP, WMS, CRM, and payment systems with hub-and-spoke middleware architecture range from $100,000–$200,000+. Legacy ERP involvement adds $15,000–$40,000 per system for the middleware layer. Here is a concrete breakdown for a mid-size manufacturer: Shopify Plus to Epicor integration with order sync ($12,000), inventory sync with ATP calculation ($10,000), pricing and catalog sync ($8,000), fulfillment and tracking integration via ShipStation ($6,000), payment reconciliation ($5,000), and B2B pricing and account management ($15,000) — total $56,000 over 10 weeks. Ongoing maintenance for this integration stack runs $1,500–$2,500/month covering monitoring, API version updates, and priority support. The ROI math is straightforward: if you are spending $80,000–$150,000 per year on manual data entry labor, eating $50,000–$200,000 in margin erosion and error-related costs, and losing sales from overselling and slow fulfillment, a $50,000–$120,000 integration investment typically pays for itself in 4–8 months. We provide detailed ROI projections during the discovery phase based on your actual transaction volumes, labor costs, and error rates.