Enter the all digits printed on the UPC bar code, including any numbers to the right or left of the bar code itself, even if they don't line up with the main row of numbers. This should be 13 digits for an EAN/UCC-13, 12 digits for a Type A UPC code, or 8 digits for a Type-E (zero-supressed) UPC code. Anything other than 8 or 12 digits is not a UPC code! (And just because it's 8 or 12 digits doesn't mean it is a UPC.) You must enter every digit here.
If you have a barcode scanner that outputs plain numbers, you should be able to use it to enter the UPC number here.