When creating a MOO product, you need to use a particular productCode parameter, used in both the call to moo.pack.createPack, and within the Pack Object Model itself. The list of valid product codes is as follows:
Round Stickers, Label Stickers, Holiday Cards, Greeting Cards and Christmas Cards are not currently supported through the API. This is because we are likely to overhaul the way that those products are created and managed, and we don't want to support the existing model going forward. Please email firstname.lastname@example.org if you want to be kept informed on this, or if you have a requirement to create the other Sticker products or Holiday cards through the API right now.