What is Amazon FNSKU?
FNSKU stands for Fulfillment Network SKU or Fulfillment Network Stock Keeping Unit.
As you already know, a SKU is a unique identifier assigned to each of your item within your marketplace.
Therefore, no two items within your entire inventory / marketplace can have the same SKU for that listing.
Similarly, Amazon assigns a FNSKU to each of your listing (a.k.a. SKU) you sell on Amazon.
When sending your items to a FBA center, you'll be able to download this code with a barcode. You have to apply it on your product so that Amazon can scan it at their warehouse.
Can SellerChamp add an item to a FBA manifest using the FNSKU?
For the first time it will not be possible to add the item using the item FNSKU.
Once you've created an Amazon FBA shipment (for that item or item included in the FBA manifest) going forward, you'll be able to add the item to your FBA manifest using the FNSKU.