1. Why Does Google Demand GTINs?
A GTIN (Global Trade Item Number, which includes UPC, EAN, ISBN) is a unique international identifier assigned by GS1. Google uses GTINs to group identical products from different retailers together in Google Shopping search results and comparison boxes.
When you sync Shopify products using the official Google & YouTube app, Shopify sends empty barcode fields if you haven't entered UPCs. Google's algorithm flags these items with:
Limited performance due to missing identifiers [gtin]Invalid value [gtin]Ambiguous identifier [gtin]
2. When Is a GTIN Actually Required vs Exempt?
| Product Type | GTIN Required? | Required GMC Identifier Attributes |
|---|---|---|
| Branded Reseller Goods (Nike, Sony, Apple) | YES (Mandatory) | gtin, brand, mpn |
| Custom / Handmade / Print-on-Demand | NO (Exempt) | identifier_exists = FALSE, brand, mpn |
| Private Label / Own Brand Products | NO (Exempt) | identifier_exists = FALSE, brand = YourBrand |
3. Step-by-Step GMC Supplemental Feed Rule Setup
Follow these 4 steps to configure feed rules inside Google Merchant Center:
- Step 1: Log into merchants.google.com and click on Products > Feeds.
- Step 2: Click on your primary Shopify Content API Feed, then navigate to the Feed Rules tab.
- Step 3: Click the + (Add Rule) button and select the attribute
identifier_exists. - Step 4: In the rule builder, set the condition: If GTIN is empty → Set to Constant Value:
no.
4. Setting Up Brand & MPN Fallbacks
When identifier_exists is set to no, Google requires at least a Brand and/or MPN (Manufacturer Part Number). In Shopify, your product SKU works perfectly as the MPN.
In Feed Rules, create a rule for mpn: Set to Extracted from Shopify SKU or Product ID.
5. Let ScaleGMC Fix Your Product Catalog
Managing complex feed rules for stores with 500+ multi-variant products can be tedious. At ScaleGMC, we build automated supplemental feed architectures that map taxonomy, fix GTIN errors, and guarantee 100% product approval.