Confused about UPC and FNSKU… Which one do I actually need on my packaging?

Hi all,

I was planning on just having my FNSKU and UPC code printed on the private label product’s packaging, but it looks like that can cause issues with the guys working at Amazon’s warehouse since they might scan the wrong code. Since these guys only need the FNSKU code, is it possible to only have the FNSKU on the packaging? Or would I need the UPC code as well for some reason?

I don’t plan to sell the product anwhere else, just on Amazon.