I have a protective box for my product that the manufacturer printed with my FNSKU. The UPC is on my product inside the protective box. If I sell to other ecommerce platforms they don't need the FNSKU instead they need the UPC. Can I put the UPC on the protective box with the FNSKU? If so, do they need to be on opposite sides or can they both be on the bottom with proper spacing? I want to utilize the protective box.

Where do I get the FNSKU barcode and is the only the barcode I put on the packaging (Not UPC code)?

For product A, when I print Item labels, the FNSKU and ASIN are same. (UPC code was used for this product).

For product B, when I print Item labels, the FNSKU and ASIN are NOT same. (UPC code was not used, exempt from UPC code).

Why is this happening and is it okay for FNSKU and ASIN to be different for a product listing without the UPC code.

Can I use this on my packaging?

Thanks!