If your product doesn’t have a UPC code on it, you will need to apply for a GTIN exception. I have done this several times and it is fairly easy and straightforward. Here are the steps:
1) Go to the GTIN (UPC, EAN…) exemption page. https://sellercentral.amazon.com/gtinx
2) Fill out the request. (Reason that you need an exemption) I included a few ASINs of similar products that had no UPC.
3) Download the appropriate template. https://sellercentral.amazon.com/gp/help/200426310
4) Fill out the template completely. Be sure to enter a SKU for each item! Have the URL for your item’s image on hand.
5) Save the completed template on your computer.
6) Click the Browse button on the GTIN exemption page and browse to your saved template.
7) Click Submit on the GTIN exemption page.
8) Wait for approval. You will receive a notice.
9) Wait another 24 hours for the approved exemption to become active. You will NOT receive a notice.
10) Go to the Add a new product page on seller central .
11) Categorize your product. It must match the category that you provided in the template in step 4.
12) Enter product details and offer. Be sure to enter the SKU that you used in step 4! Also match the brand name (if applicable) that you used on step 4.
13) Upload Images.
14) Click Save and Finish.