Reused or Duplicate Item ID in Merchant Center: Fix It

What this issue means

The id attribute is how Google tracks a product over time: its approval status, performance history and bidding data all hang on it. Google's rules:

• 1 to 50 characters, case-sensitive, but don't rely on case alone to make IDs unique
• Each different product and each variant needs its own ID
• Don't reuse an ID for a different product, and don't recycle IDs from discontinued items
• Keep the ID stable; changing it creates a new product and loses history
• Use the same ID for the same product across countries and languages; that's expected and not a duplicate
• Using the same IDs in different Merchant Center accounts is fine

A duplicate becomes a problem when the same ID represents different products, or when two sources send conflicting data for the same ID in the same country and language.

Why it happens

• Two data sources for one catalog. You connected Shopify's Google & YouTube app but kept an old XML feed or a third-party feed app running. Both send products, sometimes with different ID formats, sometimes with the same IDs and conflicting data.
• Parent SKU used for every variant. In WooCommerce or a custom feed, all sizes of a shirt share the parent SKU as id. Variants need unique IDs; the parent SKU belongs in item_group_id.
• Duplicate SKUs in your store. Two unrelated products accidentally share a SKU, and your feed uses SKU as the ID.
• Recycled SKUs. A discontinued product's SKU is reused for a new item, so Google sees a familiar ID representing a different product.
• Platform migration. Moving from WooCommerce to Shopify (or the reverse) and submitting new-format IDs while the old feed is still active.
• Case-only differences. IDs like abc-1 and ABC-1 may be treated as the same product.

How to fix it

1. Find the conflict. In Merchant Center, go to Products > Needs attention, filter for "Reused value [id]", and download the CSV. Then check Data sources to see every source that's sending products. More than one primary source for the same catalog is the usual culprit.

2. Choose one primary source per country and language. If you use Shopify's Google & YouTube app, it should usually be the only primary source for that catalog. Pause or delete leftover feed files, old app connections, or a second channel app. Use supplemental sources (keyed on the same IDs) for any extra data you need, not a second primary source.

3. Make variant IDs unique:

   • Shopify (Google & YouTube app): The app generates IDs automatically using a format based on the store's country code and the product and variant IDs, so duplicates almost always come from another source sending the same products. Remove the extra source rather than editing Shopify IDs.
   • WooCommerce: In Google for WooCommerce or your feed plugin, use the variation ID or variation SKU as id, and the parent ID or parent SKU as item_group_id. Make sure every variation has its own SKU if SKU is used.
   • Feed files: Use the variant SKU as id. A common pattern is the parent SKU plus a suffix, like TSHIRT-RED-M, with TSHIRT as the item_group_id.

4. Fix duplicate SKUs in your store. Export your products and check for repeated SKUs. Assign a new SKU to the newer product so the original keeps its history.

5. Use attribute rules if IDs can be derived. Google notes that if unique IDs can be extracted from your data, you can create an attribute rule to set unique id values in primary or supplemental sources. For example, combine SKU and a size attribute. Only do this once, and keep it stable afterward.

6. Don't rename IDs that are working. Change only the duplicates. Rewriting every ID in a catalog resets its performance history in Google Ads.

How long until it's fixed

Once the duplicate source is removed or the IDs are corrected, the issue usually clears within a few days. If you deleted a data source, the products it supplied disappear from Merchant Center when it's removed, while products from the remaining source continue. Expect Google Ads performance data to start fresh for any item whose ID you had to change.

How to prevent it

• Keep exactly one primary source per catalog, country and language.
• Enforce unique SKUs in your store, and never recycle them.
• Document your ID format and don't change it during theme or app updates.
• Before migrating platforms or feed tools, plan how IDs will map so you don't double-submit.

Duplicate sources are one of the first things we check in a feed audit because they quietly split performance and cause conflicting data. Mercantads can clean up data sources and ID structure without losing history; see our Merchant Center service, run your feed through our Merchant Center feed checker, or contact us.