E-commerce ERP Integration — The Complete Guide [2026]

E-commerce ERP integration connects your online store with the business system that runs your company — orders flow into the ERP without re-typing, and stock levels, prices and statuses flow back to the store automatically. It is the most commonly delivered e-commerce integration because it solves the two most expensive problems of selling online: stock drift (selling goods you do not have) and manual order handling (which does not scale with the number of sales channels). This guide covers what connects to what, the delivery models, real costs and the pitfalls worth designing for up front.

Key takeaway: E-commerce ERP integration links orders, stock, prices and documents between your store and an ERP system (Subiekt, Comarch Optima, enova365, SAP, Dynamics 365). Four delivery models: a ready-made connector (from 500 PLN), a hub such as Baselinker (subscription), dedicated middleware (from 4,000 PLN) or a direct API connection. A standard scope takes 1–4 weeks; non-standard B2B and multi-warehouse projects take 1–3 months. The most common pitfalls: stock drift, gross/net price confusion and orders arriving while the ERP is offline.

What e-commerce ERP integration is

An ERP (Enterprise Resource Planning) system is where a company runs sales, warehouse, purchasing, finance and accounting. An online store is one of its sales channels — and without integration it lives its own life: the store's stock count is a separate number, orders are re-typed by hand, and invoices appear only when somebody creates them.

Integration reverses that. The store becomes part of the company's system: an order placed at 2 a.m. waits in the ERP for the warehouse to open, stock updates across all channels after every sale, and sales documents are created automatically from order data. Manual work disappears — along with the most expensive error class: orders for goods that physically do not exist and documents that do not match the warehouse.

When does ERP integration make the most sense?

When at least two of these are true.

• You sell through more than one channel (store plus marketplaces plus offline sales).
• Your warehouse also serves sales outside the online store.
• You issue more than a few dozen documents a month.
• You employ — or plan to employ — someone whose main job is re-typing orders.

What connects to what — ERP systems in practice

The Polish e-commerce market has a handful of dominant ERP systems, and each one integrates differently. The table below shows real options, not sales-brochure theory.

WMS (warehouse) systems and vertical industry solutions sit next to these — they usually expose their own APIs, and the integration looks similar, but the flow scope has to be designed from scratch.

• One practical note: Subiekt GT (the older version, still very popular) has no open API as standard — it integrates through the Sfera library or file exchange. That is not a blocker, but it shapes the architecture: the work happens on the machine running Subiekt, so the integration must survive that machine being switched off.

What flows in an ERP integration

A well-designed integration defines the direction of every flow and the source of truth for every data point. In practice it looks like this.

The most common design mistake is failing to decide who owns prices. If the e-commerce team sets prices but the ERP overwrites them, a promotion can vanish on Monday morning. The decision must be made before delivery and written into the integration documentation.

Four delivery models — how to choose

The right model depends on how non-standard your process is and how deeply you want to touch the ERP.

In practice the best results come from a hybrid: a hub for commodity channels (marketplaces, carriers) plus a dedicated layer for the ERP flows where your advantage lives — stock allocation, B2B price lists, non-standard documents. I cover the hub-versus-dedicated choice in the marketplace integration guide and overall delivery costs in how much an e-commerce integration costs.

How much an ERP integration costs

Cost depends on three variables: the number of flows, how non-standard the process is, and whether the ERP has a modern API or needs workarounds.

• Ready-made connector — 500–3,000 PLN one-off plus a licence or subscription. The cheapest route, but it only covers standard scenarios.

• Dedicated integration with one ERP — from 4,000 PLN net: orders, stock, prices, documents, error handling, monitoring.

• Multi-channel integration with the ERP behind it — 8,000–30,000 PLN net: store, marketplaces, warehouse, documents, queues, reconciliation reports.

• Maintenance — from 400 PLN net per month: monitoring, reacting to API changes, small extensions.

• Honestly: the most expensive part is not the code but process analysis and testing. A company that does not know who sets prices and how stock is split between channels will pay for that knowledge in delivery hours — or twice, when the integration turns out not to fit the process.

How an ERP integration project runs

A standard project has five stages.

• Analysis (1–3 days) — mapping flows, volumes and edge cases: marketplace orders, returns, cancellations, partially fulfilled orders.
• Contract design (2–4 days) — fields, events, schedules, sources of truth, error handling and failure scenarios.
• Build (1–4 weeks) — implementation, working against the ERP test environment where available.
• Testing (3–10 days) — end-to-end scenarios on real data, failure simulations, load tests before peak season.
• Launch and monitoring — alerts, an event log and daily reconciliation reports comparing stock and documents on both sides.

For a standard scope, expect 1–4 weeks. With B2B price lists, multiple warehouses and unusual documents, 1–3 months.

The most common pitfalls

These are the problems I see most often in projects taken over from other vendors.

• Stock drift — an integration without a reconciliation report will not spot the difference until a customer buys something you do not have. A daily report is a requirement, not a nice-to-have.
• Gross and net prices — the most expensive error class. The store shows gross, the ERP calculates net, and a VAT rate change can quietly erase your margin. The conversion must be designed explicitly.
• Orders while the ERP is offline — Subiekt GT runs locally and gets switched off. A queue with retries handles this; direct API calls do not.
• Duplicate orders — a repeated webhook without idempotency creates a second order. Every endpoint must be idempotent and every message must carry an identifier.
• Promotions overwritten by the ERP — without a decision on who owns prices, every sync can break a campaign.
• API performance — Subiekt and older ERPs have limits; bulk stock synchronisation every minute can overload the system. Match the schedule to real capacity.

Good practices for resilient integrations (queues, retries, idempotency, event logs) are covered in more depth in designing resilient API and webhook integrations.

ERP integration for B2B and multi-warehouse operations

B2B selling adds requirements that off-the-shelf connectors usually do not cover.

• Individual price lists — the price depends on the customer or group; the ERP is the source of truth, and the store shows prices after login.
• Credit limits and payment terms — an order must pass validation before acceptance, not after.
• Order approvals — orders above a threshold wait for an account manager's approval.
• Multiple warehouses — stock allocation (where we ship from), reservations and transfers between warehouses.
• Documents — deferred-term invoices, credit notes, goods issue and warehouse documents.

This is the area that most often needs dedicated middleware — hubs handle the standard, but not the logic that decides your margin. Hybrid models (one catalogue, two buying paths, shared stock) are described in the B2B store guide.

Frequently asked questions

How much does e-commerce ERP integration cost?

A ready-made connector costs 500–3,000 PLN plus a licence or subscription. A dedicated integration with one ERP starts at 4,000 PLN net, and a multi-channel system with queues, monitoring and reconciliation reports runs 8,000–30,000 PLN net. Maintenance starts at 400 PLN net per month. The final price is fixed after a free scope analysis.

Can Subiekt GT be integrated with an online store?

Yes — through the Sfera library or file exchange. Subiekt GT has no open API as standard, so the integration works on the machine running Subiekt rather than in the cloud. In practice this means the message queue must survive that machine being switched off: messages wait and resume automatically. Subiekt nexo has a full API (Sfera nexo PRO) and integrates more simply.

Do I have to replace my ERP to integrate it with the store?

No. Every popular system — Subiekt, Comarch Optima, enova365, SAP, Dynamics 365 — can be integrated, although the connection architecture differs in each case. Replacing the ERP only becomes a question when the system has no data exchange mechanism at all, or its performance cannot support near-real-time synchronisation. That is a business decision, not a technical one.

How long does an ERP integration take?

A standard scope (orders, stock, prices, documents) takes 1–4 weeks from analysis to launch. Projects with B2B, multiple warehouses and non-standard documents take 1–3 months. The biggest factor in the timeline is not the code but the time needed for business decisions: who owns prices, how stock is split, how returns are handled.

What happens if the integration fails during peak sales?

A well-designed integration does not "fail" — the queue holds messages, retries them with backoff and resumes automatically. The store keeps selling; orders wait to be handed to the ERP. Two things are essential: an event log (so you know what happened and when) and an alert that fires before a customer notices a problem.

Can the integration be delivered in stages?

Yes, and I usually recommend it. Start with the highest-value flow — most often orders and stock — then documents, then extensions (B2B, additional channels). Payments are split into milestones accordingly. Value arrives after the first stage instead of after the whole project.

Who maintains the integration after launch?

Your team can — the code and documentation are yours. If you do not have a team, I offer ongoing care: monitoring, reacting to API changes on the ERP and vendor side, and small extensions. Partner APIs change several times a year, and somebody has to implement those changes so the integration does not quietly rot.

Sources and tools

• Comarch ERP Optima — documentation
• InsERT — Sfera for Subiekt (documentation)
• enova365 — developer documentation
• Microsoft Dynamics 365 — documentation
• SAP Business One — Service Layer
• PrestaShop Webservice — API documentation

👉 Want your store connected to ERP without re-typing orders? See e-commerce integrations and APIs — orders, stock, prices and documents in one consistent process. Write through the contact form or at kontakt@informatix.com.pl.

📖 See also: marketplace integration, how much an e-commerce integration costs and designing resilient API and webhook integrations.