You need a unique UPC for every "SKU." If you sell a shirt in 3 sizes and 2 colors, you need 6 unique UPC codes.
Before printing 10,000 boxes, print a sample and use a free barcode scanner app on your phone to make sure it reads correctly. buy upc codes online
Never just invent a 12-digit number. It won’t scan, and it will cause massive logistical headaches. You need a unique UPC for every "SKU
Official GS1 Company Prefixes often require an annual renewal fee to keep the codes active. Single GTINs usually do not. buy upc codes online
Visit gs1us.org. They recently introduced a "Single GS1 US GTIN" for around $30 with no annual renewal fee, making it much more affordable for small startups than it used to be.