The error is returned by Amazon API if your product data is not eligible for a new ASIN creation....
#asin/isbn
#list
#new asin creation
#product id
#sku
#synchronization
#upc/ean
If you get the error "The same Merchant SKU was found among Unmanaged Listings. Merchant SKU must...
#3rd party item
#list
#product id
#sku
#synchronization
#duplicate product
#unmanaged listings