"Error: Package weight is not valid or is missing."

To list a product on eBay, it is required to have the shipping weight. In the product details, you will see a shipping information section. There you will see a "Shipping Weight Major" and "Shipping Weight Minor". 

Make sure that you have the Major AND Minor section filled out. If your item weighs 6 ounces, put "0" in Shipping Weight Major and "6" in Shipping Weight Minor. If your item weighs 1 pound, put "1" in Shipping Weight Major and "0" in Shipping Weight Minor.