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In case the product you sell does not imply UPC/EAN (e.g. handmade, private-label), you need to get Amazon approval for listing products without Product Identifiers.
After it is obtained, you can skip indicating UPC/EAN for your product; instead, select one of the Product ID Override options in Product Identifier settings:
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None - all Products will be listed with the standard Product IDs.
All Products - Product ID exemption will be applied to all Products.
Specific Products - Product ID exemption will be applied to Products with a ‘CUSTOM’ value in the Product ID attribute. Find more details here.
Once done, indicate the None attribute for UPC/EAN.