This error is commonly referred as ‘multiple matching error’ and occurs when your Product ID (UPC, EAN, JAN, ISBN, etc.) is currently associated with two or more ASINs, but the other attributes you have provided in your inventory template (title, brand, colour, size, etc.) do not match any of these ASINs.
The provided SKU [SKU] conflicts with the Amazon catalogue. The standard product ID value(s) provided for this SKU correspond to the ASIN; however, some information is in conflict with the Amazon catalogue. Following are conflicting attribute value(s): Item Package Quantity (Merchant: [Merchant Value] / Amazon: [Amazon Value]) or Part Number (Merchant: [Merchant Value]/ Amazon: [Amazon Value]). If your product has this ASIN, modify these attributes to reflect the Amazon catalogue values. If your product has a different ASIN, check if the standard product ID value(s) are correct.
If the information in the Amazon catalogue for this product appears to be incorrect, contact Selling Partner Support.