Which number on bar code?

I’ve purchased my GTINs from GS1 and created my first product listings which are pending delivery to FBA.

These are my own private label items from the factory, and I have been granted ability to use my brand name (not brand registered yet).

When I create the barcodes for the individual packages, do I use the 14 digit GTIN that I purchased and used to create the listing or do I use the 12 digit UPC version?