Yes, you can sell your products without UPC number with GTIN apply but problem for sellers is it doesnot allow every seller and accept for GTIN exemption.
As UPC is expensive so that’s why most of sellers want to list without UPC codes and apply for GTIN exemption so if you are unable to get exemption then solution is to buy cheaper codes for listing your items at amazon from https://codesforamazon.com/product-category/barcodes/upc-barcodes/
Suggestion is to just buy cheap and working codes for amazon and list your products at Amazon to get sales.
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