Separate physical and sellable inventory
The total quantity in a warehouse is not always the amount that can be offered for sale. Reserved, damaged, return-pending and safety-stock quantities should be deducted from sellable inventory.
Keep an inventory movement ledger
Instead of changing only the latest value on a product record, log every increase and decrease with its reason, source and order number. This makes inventory discrepancies traceable.
Monitor channel updates
Sending an inventory update is not enough to call it successful. Track the channel response, error code, sent quantity and time of the last successful synchronization.
Implementation note
Adapt these principles to the API, contract and operational conditions of your sales channels. Verify critical workflows with controlled test orders before going live.