The situation
The business sold through its own site and two marketplaces. Each channel held its own stock number, updated by a scheduled export, so the site regularly sold units that were already committed to a marketplace order.
Finance had the mirror-image problem. Orders, refunds and marketplace fees arrived as separate files with separate identifiers, so the sales ledger was rebuilt every month by hand and the number never quite matched the payment provider.
What we changed
One stock position, published outward
Availability is calculated once from the operational ledger and pushed to every channel, rather than each channel keeping its own count.
Reservation at checkout, not at export
Stock is committed when the order is placed, so a second channel cannot sell the same unit.
Orders as events with one identifier
Every downstream system references the same order id, which is also what appears on the invoice and the payment record.
Returns on the original record
Authorisation, receipt and credit are steps on the order that created them, not a separate process with its own numbering.
A reconciliation a clerk can read
Orders, refunds, fees and settlements lined up per day, with unmatched items listed as a work queue instead of a variance.
We built the reconciliation report before we built the storefront integration, because it is the only thing that proves the integration is right.
How it went live
The ledger integration went first, running in parallel while finance closed two periods the old way and compared. Only when the two methods agreed on the same daily figures did the storefront start reading availability from the new source.
Marketplace channels were cut over one at a time, each with a short window where listings were frozen so the opening stock position could be established cleanly. Payment settlement matching was the last piece, once there was a stable order identifier for it to match against.
What changed afterwards
The site stopped selling stock committed elsewhere.
Month-end sales reconciliation became a report rather than a rebuild.
Refunds and fees reconcile to the settlement without manual matching.
Adding a channel is a configuration exercise, not an integration project.
