How to Fix the "Missing MPN" Error on Shopify Google Channel
Step-by-step fix for the "Missing identifier [mpn]" error in Google Merchant Center. Add MPN as a Shopify metafield or set identifier_exists to false.
What this means
When GTIN is unavailable, Google requires MPN (manufacturer part number) plus brand as the substitute identifier pair. Shopify doesn't ship a built-in MPN field, so most stores have it missing across the catalog by default — the error fires on every product Google decides should have an MPN.
How to fix it
- 1
Create a custom.mpn metafield definition
Settings → Custom data → Products → Add definition. Namespace and key: `custom.mpn`. Type: Single line text. Save.
- 2
Populate MPN per product manually for testing
Open one product, scroll to Metafields, fill `custom.mpn`. Wait 24-72h and verify the value appears in the Google channel feed before bulk-editing.
- 3
Bulk-populate via Matrixify or product CSV
Export with metafields included, fill the `custom.mpn` column for every applicable product, re-import. Use Matrixify for large catalogs; Shopify's native CSV is fragile around metafields.
- 4
If MPN doesn't exist, set custom.identifier_exists to false
Don't fabricate MPNs. For products that have no manufacturer part number — handmade, custom, private-label — set `custom.identifier_exists` to `false` and leave MPN, GTIN, and brand empty.
- 5
Verify after 24-72 hours
Force a feed re-sync (Sales channels → Google → Sync now). GMC → Products → Diagnostics → Item issues should show the MPN error cleared on affected products.
Related fixes
Related reading
FAQ
What is an MPN?+
MPN stands for Manufacturer Part Number — the manufacturer's internal SKU for a product. Different from your store's SKU unless you're the manufacturer.
Do I need MPN if I already have GTIN?+
No. GTIN is the preferred identifier and overrides the MPN+brand requirement. MPN is only needed when GTIN is genuinely unavailable.
Can I use my Shopify SKU as the MPN?+
Only if you are the manufacturer. If you resell branded products, the MPN must be the manufacturer's part number, not your internal SKU.
Why does Google want both MPN and brand?+
MPN alone is ambiguous — different manufacturers reuse part numbers. Brand plus MPN together uniquely identifies a product when GTIN doesn't exist.
Where does the Google channel app look for MPN?+
Most current versions read `custom.mpn`. Some legacy versions read `mc_google_offer.mpn`. Test by populating one product and inspecting the resulting feed.
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