The code used on the Amazon portion of the shipping label is 128B (although 128A would work since it only encodes upper case letters and numbers). I do not know what format the 2D code is in. Optional 2D box-level content codes can be of any type, but I use QR.
Its just my opinion, but if you are thinking of making your own shipping labels it’s probably not a great idea.
Although you did not ask, FNSKU barcodes are 128B (not 128A).