Almost every warehouse project is sold on picking accuracy and lands on integration. The software works; the question that decides the go-live date is whether your ERP and your WMS agree on what an article is, who owns the stock figure, and what happens when the two disagree at 4pm on a Friday.
This article sets out the actual message flow between an ERP and a warehouse management system, in both directions, plus the failure modes worth budgeting for.
In short
- Who owns what: the ERP owns commercial truth — articles, purchasing, sales, valuation. The WMS owns physical execution — location, sequence, scan, movement.
- Direction matters: master data and demand flow down into the WMS; confirmations of what physically happened flow back up.
- One owner per field. Every field needs a single system of record. Two systems both allowed to edit an article dimension is the root of most reconciliation work.
- The hard part is not the connector. It is data quality, ERP version specifics, and deciding what a failed message should do.
- Ask about your ERP version, not the product family. Versions differ far more than vendors imply.
What travels down: ERP to WMS
- Article master. Code, description, barcodes (each packaging level), unit of measure, weight and dimensions, batch/serial/expiry requirement, hazardous flags, storage conditions.
- Business partners. Suppliers and customers, delivery addresses, and any customer-specific packing or labelling instruction the floor has to honour.
- Purchase orders. The expected receipt, so goods-in can check against something instead of accepting blind.
- Sales orders. The demand, with priority, requested date, shipping method and any partial-delivery rule.
- Stock corrections from finance. Rare, but they exist — write-offs, revaluations, opening balances at go-live.
What travels back up: WMS to ERP
- Receipt confirmations. What actually arrived, per line, with the batch and expiry recorded at the dock — the trigger for invoice matching.
- Pick and shipment confirmations. What actually left, per line, with quantities, tracking numbers and carrier. This is what allows the ERP to invoice reality rather than intent.
- Stock adjustments. Counts, damages, reclassifications — every movement the ERP did not initiate.
- Return receipts. What came back, in what condition, and whether it re-entered available stock.
The full canonical list, message by message, is in the ERP–WMS message reference.
The four questions that decide the design
- Who owns the stock figure? In a healthy design, the WMS owns on-hand quantity per location and the ERP mirrors the total. If both are allowed to move stock independently, you have signed up for permanent reconciliation.
- Real time or batched? Article master can move on a schedule. Order and shipment confirmations should not: a courier cut-off does not wait for a nightly job.
- What happens to a failed message? Silent failure is the expensive answer. You want a queue, a retry, and a visible exception someone owns — not a shipment that never reached the ERP and gets discovered at month end.
- How are allocations reserved? When several channels draw on one pool, the reservation has to happen once, in one system, before the promise reaches the customer.
Where integrations actually break
- Article data that was never good enough. Missing barcodes, wrong dimensions and duplicate codes are invisible in an ERP and immediately fatal on a scanner. Cleaning them is your work, and it is the single most common cause of a slipped go-live.
- ERP version drift. A connector built for one version of your ERP may not cover the customisations layered on top of yours.
- Units of measure. One system counting pieces while the other counts cases produces stock that looks wrong by an exact multiple — easy to spot, embarrassing to find in week three.
- Partial deliveries and back orders. The rules must be identical on both sides, or the ERP re-opens what the warehouse considers finished.
- Timing at cut-off. Most disputes about "wrong" stock are two systems that were correct at different moments.
What to ask a vendor before you sign
- Do you have a pre-built connector for my exact ERP version, and how many live customers run it?
- Which messages are included as standard, and which are project work?
- Is the exchange real time or scheduled, and can we choose per message?
- What happens when a message fails — who sees it, and how is it replayed?
- Who owns each field after go-live, and what stops both systems editing it?
- What does adding a channel or a carrier cost in year two: configuration or development?
That last question predicts your running cost more reliably than the licence line. Full context on the surrounding decision is in the complete WMS guide; the ERP-versus-WMS boundary itself is covered in WMS versus an ERP warehouse module.
How BizBloqs handles it
BizBloqs runs warehouse and order execution as a configurable service next to the ERP you already have, with maintained connectors across ERP, e-commerce, marketplace, carrier and forecasting platforms — so the integration is a configuration exercise rather than a build. See the integrations overview, or book a working session and we will walk your own message flow, not a reference architecture.
