Problem
 

Inventory sync to Amazon is failing with the following error message: “Could not upload inventory information."

An FBA offer already exists on this SKU. to create a seller-fulfilled SKU, either create a new SKU or make the SwitchFulfillmentTo value MFN.
 

Solutions

This error happens if you have joined the Remote Fulfillment with FBA program (aka NARF) and some or all of your products are marked as sellable on FBA, but Extensiv Integration Manager is connected and syncing your Seller Fulfilled (MFN) inventory levels for these same products.

First, ensure that you always use a separate SKU if selling the same item on Amazon MFN and FBA. Do not sync your FBA inventory levels to Integration Manager, or if you do, disable your Amazon warehouse in Integration Manager so that inventory won't sync through.
 

Option 1: Leave the Remote Fulfillment Program
 

Option 2: Fix Offending SKUs
 

If this has happened to just a few SKUs inadvertently, you can work with Amazon to remove those specific SKUs from the FBA program. 

If you are able to split the FBA and MFN products into two completely separate listings on Amazon, this should also resolve the issue.
 

Option 3: Force MFN Inventory
 

In Integration Manager on the Amazon Cart settings page, you will find an option labeled "Force MFN Inventory." Enabling this option will make Integration Manager tell Amazon that all inventory records we send them are only for MFN products, no FBA products. This will solve the error as well.
 

Integration Manager does implement a safety measure to prevent this option from switching FBA only SKUs to MFN skus. However this can still happen if you have a single SKU that is both MFN and FBA.