To sell on Amazon, products need to be identified in your Shopify catalog to be listed on Amazon. Once identified Amazon applies a special code called an ASIN to the products.
ASINs
An ASIN (Amazon Standard Identification Number) is Amazon's unique number for a product being sold on Amazon. ASINs are unique blocks of 10 letters and/or numbers.
You will find an item's ASIN on the product detail page alongside further details relating to the item.
For example, the ASIN for Hasbro's "Monopoly" game is B00005N5PF.
https://www.amazon.co.uk/dp/B00005N5PF
If you already know the ASIN for a product you are selling you can simply use that. If you don't know it, Amazon uses your GTIN to try and find the ASIN or creates a new ASIN for you.
What is a GTIN?
A Global Trade Item Number (GTIN) is a unique identifier for trade items, developed by GS1 - “GS1 defines trade items as products or services that are priced, ordered or invoiced at any point in the supply chain”. Such identifiers usually come in the form of:
12 digit Universal Product Code (UPC)
13 digit European Article Number (EAN)
13 digit International Standard Book Number (ISBN).
Your product GTIN is represented by the product’s barcode and associated barcode number.
Without a GTIN/product identifier on Amazon, you will not be able to list your products unless you successfully apply for a GTIN exemption.
More information on GTIN and product identifiers
For further assistance, please reach out to marketplace-connect@shopify.com