Sync quantity buffer is the value Connectr subtracts from Amazon inventory before updating Shopify.
While syncing stock levels, the app uses this formula:
Shopify Inventory = Amazon Inventory − Sync Quantity Buffer
The default buffer is 0, meaning Shopify inventory matches Amazon exactly.
When an order ships, Amazon does not deduct FBA inventory immediately. The order stays Pending until status changes to Unshipped, PartiallyShipped, or Shipped—which can take from a few minutes to several hours. During that window, Amazon and Shopify inventory can temporarily mismatch, creating overselling risk.
Set a sync quantity buffer to keep Shopify inventory slightly below Amazon and reduce overselling. Configure this in Sync settings.