Auto-match one-to-one is the button at the top of the Product Mapping page. It is the fastest way to map a catalogue: it walks through your variants, looks each one up on Amazon, and saves the ASIN when it is confident. What it will not do is guess.
This is the whole feature in one sentence. Auto-match takes the barcode stored on each Shopify variant (a UPC, EAN or other GTIN) and searches Amazon's catalogue for it. Nothing else is used. It does not match on product title, SKU, brand, price or image.
That is deliberate. A barcode is a globally unique product identifier, so a barcode hit is a genuine identity match. A title is not. "Blue running shoe, size 9" will happily return a dozen plausible looking products from three different manufacturers, and if the app picked one for you, you would spend the next month reading a competitor's price and thinking it was yours.
The "one-to-one" in the name is the rule that governs the whole run. For each variant:
Auto-match never picks the "best" of several candidates, and never picks the first one. A wrong ASIN is worse than no ASIN, because a wrong ASIN looks finished. It shows a green Mapped badge, it writes a price into your Shopify metafields, and your storefront will happily show a shopper a price for a product you do not sell. An unmapped variant, by contrast, is visibly unfinished and sits in your Needs mapping filter waiting to be dealt with.
Auto-match respects the screen you are looking at, within two limits:
Existing mappings are left alone. Auto-match only fills in blanks.
When the run finishes you get a banner in this form:
Scanned 240, matched 168, no result 51, multiple 14, failed 7.
Here is what each number is telling you, and what to do about it.
Scanned is how many variants were examined. If this is far lower than your catalogue size, check the Active only checkbox and your plan cap first.
Matched is the number of new mappings saved. These rows now carry an ASIN and will start pulling prices on the next price sync. Press Sync on a row if you want a price immediately.
No result means the barcode was searched and Amazon returned nothing. Usually the product is genuinely not on Amazon, or the barcode in Shopify is wrong, mistyped, or is an internal code rather than a real GTIN. Check the barcode against the physical product, then map by hand if the product does exist on Amazon under a different identifier.
Multiple means the barcode returned several Amazon products. This is common with multipacks, bundles, and products where several sellers have created duplicate ASINs for the same item. These need a human decision. Open the row, click Map, search the barcode again, and choose the ASIN you actually compete on (normally the one with live offers and reviews).
Failed means the lookup errored rather than returning an empty answer. Usually this is Amazon throttling the app during a large run. Simply run Auto-match one-to-one again. Anything already matched is skipped, so a second pass is quick and cheap.
A variant with no barcode can never be auto-matched. There is nothing to search with. These appear under the No barcode filter pill and carry the No barcode status badge, and they are not even counted as scanned.
You have two options:
Note
Barcodes and SKUs are edited on the Shopify product page, under the variant's details. They are never edited inside Amazon Seller Sync. The app only reads them.
Tip
Auto-match is safe to re-run as often as you like. It is idempotent: it only ever fills in unmapped variants. Running it after a bulk barcode cleanup in Shopify is the normal way to pick up the stragglers.