UPC numbers are required for some of our new products, so we added a UPC text input attribute to our magento installation. However, our new UPC attribute will not display under the drop-down list of available attributes to choose from when in the M2E listing settings for the UPC option. There are very few attributes that do display there. So, we deleted the attribute entirely and then went back to M2E section and clicked on the "create new attribute" option at the bottom of the UPC drop-down and created a new attribute through the M2E interface, assuming since we used their interface and it was associated with the UPC drop-down field, it would work that way. However, it still does not display in that UPC attribute field drop-down. Please explain how we get it to display as an available attribute for the UPC field in M2E listing template settings.