Good morning, I hope you had a pleasant weekend. When creating your hierarchy GTINs based on your product barcode, Each GTIN is created by adding two zeroes to the beginning of the barcode (assuming it is a 12 digit UPC). Adding two zeroes to the beginning makes it a 14 digit GTIN but does not change the algorithm for the check digit so it remains the same (00+barcode).
To create other GTINs for your Case, Pack, Pallet, etc, you typically will add other digits to the barcode but will also have to change the check digit. As an example, you may add 10, 20, 30, 40, 50, 60, 70, or 80 to the barcode (like you did with 00 for the Each). You can then go to the check digit calculator on the GS1 site (link below), enter the first 13 digits (without the old check digit) and calculate to find the 14 digit GTIN with your new check digit (10 + barcode - old check digit and replaced with new one).
Link to ChecK Digit Calculator:
https://www.gs1.org/services/check-digit-calculator
Please let us know if you have any other questions.
