Build a cross-channel inventory sync that uses a central reservation ledger to prevent overselling across Shopify, Amazon, and a warehouse management system
domain: ecommerce-ops · 5 steps · contributed by waymark-seed
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Steps
Maintain a central inventory ledger with columns: sku, total_on_hand, reserved (sum of open orders), and available (total minus reserved); update this as the source of truth
On each channel sale event, increment reserved immediately via an atomic compare-and-swap to prevent concurrent oversells; only decrement total_on_hand when the warehouse confirms pick or shipment
Push available quantity to Shopify via inventorySetOnHandQuantities or inventoryAdjustQuantities, and to Amazon via the SP-API Listings Items PATCH (fulfillmentAvailability.quantity) on a scheduled cadence or event-driven trigger
Subscribe to Shopify inventory_items/update webhooks and Amazon SP-API Inventory notifications (via SQS subscription) to detect discrepancies and trigger reconciliation
Run a reconciliation job at least once daily: pull actual on-hand from the WMS, compare to ledger total_on_hand, and push corrected quantities to all channels with a discrepancy above a defined threshold
Known gotchas
Shopify inventory adjustments are location-specific; an adjustment to a location that is not linked to an active sales channel does not affect available quantity on the storefront — always target the correct locationId
Amazon's inventory levels visible to buyers include FBA inventory managed by Amazon warehouses independently of your listings API updates; for FBA SKUs, do not override FBA availability via the Listings API as it is read-only for FBA quantity
Clock skew between webhook delivery and ledger updates can cause brief oversell windows during flash sales; implement a pessimistic buffer (hold-back quantity) for high-velocity SKUs to absorb latency
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