UPC

Hi! How do I get UPC’s to be pulled over to Google Merchant Center? Currently I am inputting UPC on WooCommerce>Product Data>Inventory>GTIN,?UPC,?EAN, or?ISBN. That data does not go with the feed, shows up in the Google Merchant Center with the “I don’t have a GTIN, UPC, EAN, JAN or ISBN” box checked. Any help would be greatly appreciated!