About the Google Shopping Product identifiers requirements

Include unique product identifiers in your product data
Depending on the type of product you submit, you'll submit different identifiers. For all your items, we recommend submitting all three attributes (gtin, brand, and mpn) to help boost ad performance and help users find your products.

Use the following set of rules to provide the correct identifiers for each of your products.

New products with GTINs
For all new products (which is submitted with the condition attribute) that have a GTIN assigned, submit the following attributes:

- gtin
- brand
- mpn (recommended)

Products without a GTIN
Some products don’t have a GTIN assigned, and so you don’t need to submit one. However, if the product does have a GTIN assigned and you don’t submit it, then the product could be disapproved.

For these products, submit the following attributes:

- brand
- mpn

Examples of products that may not have an assigned GTIN include:

- Store brand products
- Replacement parts
- Original equipment manufacturer (OEM) parts or replacements for OEM parts
- Custom-made products (e.g., custom t-shirts, art, and handmade goods)
- Books released before ISBN was approved as an ISO standard in 1970
- Vintage or antique products
- Preorder products (using the condition attribute) 
- For products without a GTIN and brand nor mpn and brand, submit identifier_exists.

Products without a brand
If the product has a clearly associated brand or manufacturer, submit the brand attribute.

However, you don’t need to submit the brand attribute if the product doesn’t have a clearly associated brand (e.g., movies, books, and music) or is a custom-made product (e.g., custom t-shirts, art, and handmade goods).

Go to the official Google Shopping Feed product identifier specifications