A supplemental feed lets you add or change product attributes in Merchant Center without touching the data Shopify sends. When it does not match up, Merchant Center shows "Missing product in primary feed" and rejects the update for that item. This guide explains what a supplemental source does, why the issue appears and how to set one up correctly.
What a supplemental source does
Google describes a supplemental data source as a secondary source that adds details or updates existing ones in your primary source. On a Shopify store, the primary source is usually the product data from the Google & YouTube channel. It is useful for attributes Shopify does not send the way you want, such as custom labels.
- ✅ Add or update attributes on products that already exist
- ❌ Add new products
- ❌ Remove products
- ❌ Work as a standalone source
What the issue means
"Missing product in primary feed" means one or more items in your supplemental source do not exist in the primary source, so there is nothing to update. Google's example is a price change for an item that was never uploaded successfully through the primary feed.
- Effect: The update for that item is rejected
- Usual cause: An ID that does not exactly match the primary source
- Other causes: A different target country, or the product itself failed in the primary source
Set it up
Google says the Supplemental sources tab only appears after you turn on the Advanced data source management add-on, under Settings and then Add-ons. Then follow these steps.
- Open: Settings, then Data sources, then the Supplemental sources tab
- Add: Select Add supplemental product data
- Input: A file, a Google Sheets template or the API
- Link: Enter the details, choose the primary data source, then select Create data source
Google says to match your product ID from the primary source exactly, and to make the data source label and language match too. The safest way to get the right IDs is to download your products from Merchant Center and copy the IDs from there, rather than typing Shopify SKUs or product numbers.
Find and fix rejected items
In Merchant Center, open Products, go to the Needs attention tab and filter by the issue name. Download the affected items as a .csv file and compare each ID with your primary product data.
| Check | Fix |
|---|---|
| ID differs from the primary source | Copy the exact ID from Merchant Center |
| Different target country | Select the same country in both sources |
| Product missing from primary source | Fix the primary source before the supplemental one |
Keep it working
A supplemental source keeps overriding the primary one until you change it, so a stale sheet can quietly undo changes you make in Shopify. If you need an attribute changed for every product, Google's attribute rules may be simpler than a sheet. For context on feeds in general, see what a product feed is.
- ✅ One sheet per purpose, such as labels only
- ✅ Remove rows for products you have deleted
- ❌ Price or availability in a sheet nobody updates
Doing this at scale
FeedFix checks every product against Google Merchant Center and Meta Catalog rules and scores each one from 0 to 100 per channel, so you can see which products have data problems. It drafts compliant title and description rewrites you review as before/after diffs, apply in bulk, and every change is audit-logged. See FeedFix.