Amazon requires you to list your product with a barcode (EAN, UPC, ISBN). If you do not have barcodes for your products, you can apply for a GTIN exemption so that you can list without this.
It is useful if you have a large inventory or custom products.
If you have only a few products it may be easier to purchase barcodes from a reseller (e.g. barcodestalk.com)
Eligibility
To apply for a GTIN Exemption, you will need to complete a letter of authorisation which confirms the products do not have any barcodes: See template here:
EAN exemption form.doc
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Sample Letter
You'll need to get this letter on company headed paper.
You also need to know the category of your products and the exact brand name as used on the Amazon listing