How to Integrate ERP, CRM and E-commerce Systems Without Creating Three Versions of the Truth

A business starts selling online, and for a while someone copies each web order into the stock spreadsheet and the accounting package. Then orders double. Stock shown on the site is wrong by lunchtime, a customer is charged for something that sold out yesterday, and the sales team has no idea a regular buyer just placed three orders on the website. The answer is integration. Done carelessly, it produces a different problem: three systems, each confidently holding a different version of the same order.

This guide sets out the method we use. It applies whether the store runs on Shopify, WooCommerce or custom code, and whether the ERP and CRM are packaged products or built for you.

Step 1: decide which system owns each record

Most integration problems are ownership problems. If a price can be edited in both the store and the ERP, sooner or later the two will disagree and nobody will know which is right. For each kind of record, name one system as the master. Changes are made there and copied outwards, never the other way.

Step 2: map what flows, and in which direction

• Stock: ERP to store. Updated on every stock movement or every few minutes, with a safety buffer on fast-moving items so the last unit is not sold twice.
• Orders: store to ERP. Each paid or cash-on-delivery order creates a sales order in the ERP, reserving stock immediately.
• Fulfilment: ERP to store. When the order is packed and handed to the courier, the tracking number goes back to the store, which notifies the customer.
• Customers: store to CRM. A new buyer becomes a contact, and each order is added to their history, so sales and support can see it.
• Returns and refunds: both ways. A return approved in the store must put stock back and raise a credit note in the ERP.
• Payments: gateway or courier to ERP. Card settlements and cash-on-delivery remittances are matched to invoices, which is where the money is actually reconciled.

Decide for each flow whether it must be immediate or can run on a schedule. Stock and orders usually need to move within minutes. A nightly run is fine for product descriptions and accounting summaries.

Step 3: choose how to connect

Start with a connector if a good one exists for your two products, and check its reviews for the exact flows you need, particularly multi-location stock, bundles, partial shipments and refunds. Move to a custom integration when you find yourself working around the connector more than using it. Shopify, WooCommerce or custom covers how the platform affects this choice.

Step 4: plan for failure

Every integration fails sometimes. An API is down for ten minutes, a product code exists in the store and not in the ERP, a customer's address has a character the other system rejects. What separates a reliable integration from a fragile one is what happens next.

• Queue and retry. A transfer that fails is kept and tried again, not dropped.
• No duplicates. Each order carries a unique reference, so sending it twice creates one order, not two.
• Alert a person. After repeated failures, someone is told, with the reason in plain words.
• An error screen. Staff can see what is stuck, fix the cause, such as a missing product code, and resend.
• A log. Every transfer is recorded with its time and result, so a dispute can be traced.

Step 5: reconcile every day

Even a well-built integration can miss something. A short daily report that compares the systems catches it within a day instead of at month end: the count and value of orders in the store against sales orders in the ERP, stock quantities for a sample of products, and payments received against invoices. The same principle for the ledger is explained in integrating accounting software with an ERP.

A sensible order of work

Mistakes that cause the most trouble

• Allowing prices or stock to be edited in two systems.
• Matching products by name instead of by code.
• Syncing stock once an hour on products that sell every few minutes.
• Forgetting returns, cancellations and partial shipments until after launch.
• No error screen, so failed orders are discovered when a customer complains.
• Testing only with simple orders. Test with discounts, bundles, multiple warehouses and refunds.

We build these integrations as part of our ERP and CRM and e-commerce work, and for existing systems that were never connected. Tell us which systems you run and we will map who should own what before anyone writes code.