OK, so after weeks of frustration, I may have solved this tonight by myself. When a product shows up in the Needs Attention tab, and the problem is that Printful doesnt provide a GTIN or MPN, do not click on the FIX or Needs Attention tab. Instead, go into Edit Product and look for the button that says "I don't have a GTIN, UPC, JAN, or ISBN." That will give you an option to select saying it is a one-of-a-kind product. Printfuls print on demands products count as custom one of a kind products. Select that and save. It's working for my products, where as the Needs attention and fix options did not work!
