Still updating stock levels by hand? How webshop-ERP stock sync actually works

The manual routine

The setup: products sell in the webshop — Shopify, WooCommerce, Centra. Stock truth lives in the ERP — Fortnox, Visma, Business Central — because that’s where purchasing, goods receipts, and returns are booked. In between, someone keeps the two aligned by hand: check the warehouse balance in the ERP, update the quantity in the webshop, repeat for every product that moved.

Unlike order import, this job has no natural rhythm. Stock changes when something sells, when a delivery arrives, when a return comes back, when a B2B order ships from the same shelf. Manual sync means picking a frequency — every morning, twice a week — and accepting that the webshop is wrong in between.

How merchants compensate for stock they can’t trust

Most shops running manual stock sync have already made peace with it, usually through some combination of three workarounds:

The buffer. Show fewer units than the warehouse holds — if the ERP says 10, the webshop says 6. Overselling gets rarer; so do sales. Every buffered unit is stock you paid for but won’t sell online today.

The early sold-out. Mark products out of stock while units remain, because running to zero online feels riskier than leaving sales on the table. Same trade, larger denomination.

The morning check. Someone opens the ERP with their coffee and walks the list. Reliable at 30 products; fiction at 3,000.

All three are rational responses to the same problem: the webshop’s number can’t be trusted, so the merchant trades revenue for safety. The cost is invisible precisely because it’s a non-event — the sale that didn’t happen doesn’t show up in any report.

When the workarounds break

The pressure peaks exactly when the shop is winning. Campaigns and Black Friday compress days of normal volume into hours — and high order volume is precisely when stale stock levels turn into oversold orders. Two customers buy the last unit, and now support is writing an apology email and processing a refund for a product that never existed. The one week the buffer was supposed to protect is the week it’s least sufficient.

The Politecnico di Milano research cited earlier in this series puts numbers on the baseline problem: SMBs running disconnected systems report a 3–5% data error rate, and wrong stock levels are one of the two places it shows up (incorrect invoices being the other).

What stock sync actually does

With an integration platform between the systems, stock sync is a scheduled flow with a clear direction:

1. The ERP stays the single source of truth. Purchases, goods receipts, returns, and B2B orders all land in the ERP — so that’s where the real balance lives. The sync’s job is to make the webshop follow it, not the other way around.

2. A scheduled sync picks up the changes — every five minutes by default. Stock is a state, not an event: what matters is that the webshop converges on the ERP’s truth quickly and continuously, without anyone triggering anything.

3. The quantity is updated in the webshop via the API. Each product’s sellable balance lands in the shop — mapped by SKU, across every product that moved since the last run.

That’s the whole flow. It’s less dramatic than the order webhook from the first article in this series — deliberately. Stock sync is plumbing: its job is to be boring, frequent, and correct.

What changes in practice

The buffer can shrink toward zero, because the webshop’s number is minutes old instead of days old. The early sold-outs stop, because running low online no longer requires courage. And the morning check disappears entirely — the list walks itself.

There’s an honest caveat, and it’s the same one that applies to any interval-based sync: five minutes is not zero. In an extreme flash-sale scenario — hundreds of orders in minutes on a single product — even a five-minute-old number can lag reality, which is why high-volume campaign setups are worth a configuration conversation before the event rather than after. For everyday operations, including a normal Black Friday, minutes-old stock is the difference between guessing and knowing.

If someone in your company still updates webshop quantities by hand — or if your buffer exists because the alternative is apology emails — the question is the usual one: