With Amazon FBM, you hold the stock - so inventory syncs one-way from Katana to Amazon, the opposite direction of the Amazon FBA integration. Katana is the source of truth, and your FBM listing quantities on Amazon follow what's available at your chosen fulfillment location.
When Katana pushes stock to Amazon
The push is real-time and event-driven - there is no schedule and no sync window. Whenever a stock event changes the available quantity of an FBM-mapped variant (a sale, a purchase order receipt, a stock adjustment, a completed manufacturing order, a stock transfer, or a return), Katana recalculates the quantity and sends it to Amazon immediately.
If several changes happen in quick succession for the same SKU, Katana pushes the latest value - your listing always ends up with the current number
Only variants mapped to Amazon FBM are pushed. Variants mapped to Amazon FBA are managed by the FBA integration and are not affected
Which stock value is sent
In the Inventory settings section of the FBM configuration page, choose the stock value Katana sends to Amazon:
In stock (default) - the quantity physically available at your FBM fulfillment location. The safe choice if you only want to sell what's already on the shelf
In stock + Expected - also counts stock you're expecting from open purchase orders. Useful when supplier lead times are reliable and you want listings to stay active through replenishment cycles
In both cases, Katana excludes stock that's already committed to other orders and never sends a negative number - if the calculation would go below zero, Amazon receives 0.
Kits and bundles push Potential (buildable) stock
Kit and bundle items - products with a bill of materials (BOM) - follow their own rule automatically: Katana pushes their Potential stock, the quantity you can build right now from available components, instead of the stock value selected above.
This means a made-to-order product can stay sellable on Amazon even with zero finished units on the shelf - as long as you have the components to build it. This behavior is automatic and not configurable.
Sync history and troubleshooting
Every push is logged. Open Inventory sync history on the FBM configuration page to see what was sent, when, and whether Amazon accepted it.
If a push fails temporarily (for example, an Amazon rate limit), Katana retries automatically - you don't need to do anything
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