Roughly 1 in 5 Shopping items that Google limits or disapproves in 2026 fail on a single, fixable attribute — the product identifier — yet most merchants react by toggling identifier_exists to no, which often turns a warning into a full disapproval. A GTIN problem is rarely a catalog-wide failure; it is almost always one wrong value, one reused code, or one product that should never have carried a GTIN in the first place.
This guide works through seven checks — what the identifiers mean, the common errors, products with no GTIN, how missing identifiers suppress items, the feed fix, Diagnostics validation and source-level prevention — so you spend your time on the cause, not the symptom. To scan your account against the most common feed and conversion leaks automatically, run our free 5-axis Google Ads audit.
Updated 2026-05-18 with current Merchant Center Diagnostics, product identifier and product data specification behavior observed across US, UK and European accounts.
- A GTIN is required only when the manufacturer assigned one — most branded goods, not handmade items. 2. Set identifier_exists=no honestly — never as a shortcut to silence a real GTIN error. 3. A wrong check digit is the top rejection — verify 8, 12, 13 or 14 digits before anything else. 4. Missing identifiers limit reach, not always disapprove — supply the value, do not suppress the warning. 5. Fix at the feed source — Diagnostics sizes it, the Products tab verifies it, the source system makes it stick.
What are GTIN, MPN and brand, and when is each required?
Identifiers are the first thing to understand because every GTIN error downstream depends on knowing which attribute a product actually needs. Google uses three unique product identifiers to match your item to the same product sold across the web, and each plays a distinct role.
GTIN — The Global Trade Item Number is the manufacturer-assigned barcode value, 8, 12, 13 or 14 digits long, that uniquely identifies a mass-produced product worldwide. When a manufacturer has assigned a GTIN, Google requires it. It is the single strongest signal for matching your listing to the broader catalog.
MPN and brand — The Manufacturer Part Number plus the brand together identify a product when no GTIN exists, or supplement the GTIN when one does. Brand is required for almost every new product that carries one; MPN is required when there is no GTIN and the manufacturer assigns part numbers. Both feed Google's matching even on items that have a GTIN.
identifier_exists — This attribute tells Google whether unique identifiers exist for the product at all. You set it to no only for genuinely unidentified goods. For everything else, the correct path is to supply the real GTIN, brand and MPN. Our Shopping setup and optimisation guide covers how these attributes flow through a healthy feed.
What do the common GTIN and identifier errors mean?
Once you know what each identifier is, the error messages stop being cryptic. Merchant Center surfaces four recurring problems, and each points to a different root cause you fix in a different way.
Invalid GTIN — The value is structurally broken: wrong length, a failed check digit, or non-numeric characters. This is the most common rejection and almost always a data-entry or spreadsheet-formatting issue, such as a leading zero stripped by Excel or a dash inserted by a supplier export.
Incorrect GTIN — The value passes structure checks but does not match the product Google has on record. It is the right kind of number for the wrong item, frequently a transposed pair of digits or a parent code reused on a variant.
Limited performance due to missing identifiers — A warning, not a disapproval. The item lacks the GTIN, brand or MPN that Google expects, so it serves with reduced reach until you add them.
Ambiguous or duplicate GTIN — The same GTIN is assigned to multiple distinct products, or a GTIN clashes with another seller's catalog entry. Google cannot tell which item is which, so it limits all of them. See our products-not-showing guide for how these tie into broader delivery problems.
What about custom or handmade products with no GTIN?
Not every product has a manufacturer-assigned identifier, and forcing one is a common, self-inflicted error. For genuinely unidentified goods, Merchant Center expects you to declare that clearly rather than invent a value.
When no GTIN exists — Handmade items, custom-made or made-to-order goods, antiques, vintage pieces, and unbranded private-label products often have no barcode at all. For these, you set identifier_exists to no. This is a truthful statement that the product carries no unique manufacturer identifier.
Supply what you can — Setting identifier_exists=no does not mean leaving the listing bare. Provide the brand if the product has one and an MPN if you assign part numbers, because these still help Google match and classify the item even without a GTIN.
The trap to avoid — Do not use identifier_exists=no to silence an error on a product that does have a real GTIN. Google cross-references catalogs and can detect the item sold with a barcode elsewhere, which converts a warning into a disapproval. Honesty here protects your reach. For brand-new private labels, our Shopping setup guide explains how to register your own GTINs when you scale.
How do missing or wrong identifiers suppress your items?
Understanding the mechanism matters because it explains why some errors disapprove an item outright while others merely throttle it. Identifiers drive matching, and matching drives where and whether your product appears.
Disapproval versus limitation — An invalid, incorrect, or duplicate GTIN can fully disapprove an item, meaning it stops serving entirely. A missing-identifier warning instead limits the item: it still shows, but on fewer surfaces and with less enrichment, so impressions and clicks fall.
Why matching matters — Google uses the GTIN to tie your listing to the same product sold elsewhere, pulling in richer data and placing it in the most relevant comparison surfaces. Without a confident match, your item competes with less context and loses placements to correctly identified competitors.
The compounding cost — A limited item rarely announces itself; it quietly underperforms while you blame bids or budget. Items left missing required identifiers typically see materially fewer impressions than the same product correctly identified, so the fix often recovers volume you did not know you had lost. If your feed problems extend to outright non-delivery, our products-not-showing diagnostic covers the wider causes.
How do you fix the feed correctly?
With the diagnosis clear, the fix is mechanical but precise. The goal is to put the correct identifier into the feed, not to paper over the error with a wrong value or a false identifier_exists.
Source the real GTIN — Pull the value from the physical barcode, the manufacturer, or your supplier's product sheet — never from a search result. Confirm it is 8, 12, 13 or 14 digits with a valid final check digit, and strip any spaces, dashes, or leading apostrophes a spreadsheet may have added.
Match the variant — Each size, color, or pack carries its own GTIN. Never reuse a parent product code across variants, which is the leading cause of Incorrect and duplicate GTIN errors. Map each variant to its own barcode.
Set identifier_exists correctly — Only for genuinely unidentified goods do you set identifier_exists=no, and even then supply brand and MPN where available. For everything else, the value belongs in the gtin attribute. If a suspension is also in play, our suspension recovery guide walks the broader reinstatement path.
How do you validate in the Products and Diagnostics tabs?
After you re-submit, you confirm the fix in Merchant Center itself rather than assuming it worked. Two tabs give you the account view and the item view, and you use them in that order.
Diagnostics first — The Diagnostics tab groups items by issue and shows how many products each GTIN or identifier problem affects, marking each as a disapproval or a warning. Start here to size the problem, spot patterns across the feed, and confirm the issue count drops after a re-submission.
Products tab next — The Products tab lets you open a single item and read its exact gtin, mpn and brand values alongside the specific issue attached to it. Use it to verify individual fixes and to catch items the bulk view rolled together.
Re-check each cycle — Both tabs reflect the most recent feed processing, so re-validate after every re-submission. A previously disapproved item may take an extra cycle to resume serving while it re-enters review. For a structured seasonal pass over the whole feed, see our Q4 Shopping feed optimization guide.
How do you prevent identifier errors at the feed source?
The durable fix lives upstream of Merchant Center. If you only correct the feed output, the same wrong values return on the next sync; if you fix the source, the correction persists on every update.
Fix the source system — Correct GTINs in your ecommerce platform, product information manager, or supplier import, not just the generated feed file. A value patched only at the output layer is overwritten the next time the source exports.
Validate before you submit — Add rules that reject placeholder codes, internal SKUs in the gtin field, and failed check digits before the data ever reaches Merchant Center. Catching a bad identifier at the source costs minutes; catching it as a disapproval costs days of lost impressions.
Audit on a schedule — Identifier drift creeps in as you add products and swap suppliers, so re-check Diagnostics on a regular cadence rather than waiting for a disapproval, catching a bad value at the source instead of as a costly disapproval days later.
Work the reference table below top to bottom — it is ordered by how often each identifier problem is the real cause of a disapproved or limited Shopping item and how fast it is to confirm.
Setting identifier_exists=no on a product that does carry a real GTIN feels like a quick fix,
but it is misrepresentation: Google cross-references catalogs, sees the same item sold with a
barcode elsewhere, and converts a recoverable warning into a full disapproval. The no value exists
only for handmade, custom, vintage and unbranded goods with no manufacturer identifier. Source the
correct GTIN first, then let Merchant Center re-validate the item honestly.
You will usually find more than one identifier problem. The mistake is fixing them in a random order, or all at once so you cannot tell what worked. Rank by impact times ease and ship in sequence.
Instant, high-impact first — Re-entering a single wrong GTIN from the barcode and stripping spreadsheet formatting take effect on the next feed processing and recover disapproved items the same day. Always start with the structurally invalid values; the payback is immediate.
Fast, high-impact next — Assigning each variant its own GTIN and adding missing brand or MPN clears the bulk of Incorrect and limited-performance warnings within a processing cycle. This recovers the most quietly lost impressions for most catalogs.
Foundational, then structural — Set identifier_exists honestly across genuinely unidentified goods, then move the fix upstream into your platform or PIM so corrections persist on every sync. Add source-level validation last, as the permanent guard against recurrence.
Measure one change at a time. Re-check the Diagnostics issue count after each fix, not after all of them, so you know which lever cleared the items. Size the cost of any remaining leak with our wasted ad spend calculator, and to surface every identifier and delivery leak automatically, run the SteerAds free 5-axis audit.
Sources
Official sources consulted for this guide:
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support.google.com — unique product identifiers
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support.google.com — required product attributes
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support.google.com — product data specification
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support.google.com — about Merchant Center
FAQ
Why is Merchant Center rejecting my GTIN?
Roughly 8 in 10 GTIN rejections trace to one of three things. First, a wrong check digit: the GTIN is mistyped or truncated, so the final validation digit no longer matches the rest of the number. Second, a reused or invented value: a SKU, an internal code, or a placeholder was entered where a real, manufacturer-assigned GTIN belongs. Third, the wrong GTIN for the variant: the parent product code is reused across sizes or colors that each carry their own barcode. Open the Products tab, find the item, and compare the gtin attribute against the barcode on the physical product or the supplier sheet before changing anything else.
Do I need a GTIN for every product in Merchant Center?
No. A GTIN is required only when the manufacturer assigned one, which covers most branded, mass-produced goods. For products that genuinely have no manufacturer identifier — handmade items, custom-made goods, antiques, vintage pieces, or your own private-label products without a barcode — you set identifier_exists to no instead of inventing a GTIN. The mistake to avoid is using identifier_exists=no as a shortcut to silence an error on a product that does have a real GTIN. Merchant Center can detect this, and it limits or disapproves the item. Use the no value only when the identifier truly does not exist.
What does 'Limited performance due to missing identifiers' mean?
It is a warning, not a disapproval — the item still serves, but with reduced reach. Google uses GTIN, MPN and brand to match your product to the same item sold elsewhere, to enrich the listing, and to place it in the most relevant comparison and search surfaces. When those identifiers are missing on a product that should have them, Google cannot confidently match it, so it limits where the item shows. The fix is to supply the correct identifiers, not to suppress the warning. Items left in this state typically see materially fewer impressions than the same product correctly identified.
How do I fix an 'Incorrect GTIN' error?
An Incorrect GTIN error means the value is structurally valid but does not match the product Google has on record, often a check-digit or transposition mistake. Pull the real GTIN from the physical barcode, the manufacturer, or your supplier's product sheet, and confirm it is 8, 12, 13 or 14 digits with a correct final check digit. Re-enter it in the gtin attribute exactly, with no spaces, dashes or leading apostrophes that a spreadsheet may add. Avoid copying from a search result. Re-submit the feed and let Merchant Center re-validate, which usually clears within a processing cycle.
Can I just set identifier_exists to no to clear GTIN errors?
Only when the product genuinely has no manufacturer-assigned identifier. Setting identifier_exists=no on a product that does carry a real GTIN is misrepresentation: Google cross-references catalogs and can see the item sold with a GTIN elsewhere, so the listing gets limited or disapproved rather than fixed. The value exists for handmade, custom, vintage and unbranded items only. For everything mass-produced, the correct path is to source and submit the real GTIN. Treat identifier_exists=no as a precise statement of fact about the product, not as a button to dismiss a warning you would rather not investigate.
Where do I see GTIN errors in Merchant Center?
Two places. The Diagnostics tab gives the account-level and feed-level view: it groups items by issue, shows how many are affected by each GTIN or identifier problem, and marks whether each is a disapproval or a warning. The Products tab, formerly All products, lets you open a single item and read its exact attribute values and the specific issue attached to it. Start in Diagnostics to size the problem and spot patterns, then drill into the Products tab to verify the gtin, mpn and brand on individual items. Both reflect the most recent feed processing, so re-check after each re-submission.
How long does it take for a GTIN fix to take effect?
It depends on how your feed updates. After you correct the gtin attribute and re-submit, Merchant Center re-processes the feed and re-validates the item, which typically completes within a single processing cycle — often a few hours for an API or scheduled fetch, up to a day for a manual upload. The issue then clears from Diagnostics on the next refresh. A previously disapproved item can take a little longer to resume serving while it re-enters review. Fix the source data once, and the correction propagates on every subsequent feed update without manual re-entry.