Amazon has both a SKU and an FNSKU data ID for each of your listings. The SKU is your free-form text you use to identify “this” listing. The FNSKU is Amazon’s generated data for THEM to identify your item in their warehouse system. They are not interchangeable when referring to them. FYI
In the Send to Amazon Workflow, Amazon only offers to print labels for listings that have had Amazon Barcode selected instead of Manufacturer’s Barcode for identification in the system. This is set as default in Seller Central, Settings (Gear Icon upper-right) under Fullfillment By Amazon, Label Preferences.
Once selected for an ASIN, it can’t be changed without either creating another listing, or deleting the existing and re-create it after waiting 24 hours and using he original SKU. Changing the default is not retro-active.
You can tell which type in Seller Central, Inventory, Manage All Inventory. Look at the FNSKU there.
If it is the same as the ASIN, it is Manufacturer’s Barcode and you won’t be offered to print labels. This is because Amazon expects a UPC barcode. If it is scannable, no label is needed.
If it starts with X00, it is Amazon Barcode and will require a label and you will be offered to print one.
You can always print FNSKU labels from the Manage All Inventory page. In the Edit Menu at the right, choose Print Item Labels. You can’t print labels for FBM listings.
So, what is the difference?
Manufacturer’s Barcode uses the existing UPC barcode to identify the item in the warehouses. However, your items will be co-mingled in bins with all other listings with that barcode. This allows Amazon to choose someone else’s item in a different warehouse that is closer to the buyer. The advantage is that you don’t have to re-label anything.
The X00 barcode items will be stored in their own separate bins. The advantage is that the buyer will get your items as you prepped them. The disadvantage is that you have to re-label every item.
I hope this helps.