Shuttle tried to update a product's stock on Etsy after a change in Shopify, but it could not find the Etsy listing that goes with it. The Etsy stock was not changed.
Why it happens
The product is not matched to an Etsy listing. It was never transferred to Etsy and was never matched. On the Products page, use the Unmatched filter to check.
The Etsy listing was deleted. The product was matched before, but the listing is no longer in your Etsy shop. Look for it on Etsy.
Shuttle could not find the listing by SKU. Shuttle finds a listing by SKU only when "Match products and variations by SKU" is turned on and the SKUs are the same in both shops.
A bundle sold on Etsy, and one of its items is not on Etsy. When a Shopify bundle sells on Etsy, Shuttle also updates each item in the bundle on Etsy. If an item, or one of its variations, has no matched Etsy listing, you see this error for that item.
How to fix it
Go to Products and use the Unmatched filter to find the product.
If the product is already on Etsy, match it. See Matching Products & Variations.
To let Shuttle match by SKU, go to Settings > Products > General and turn on "Match products and variations by SKU". Make sure each SKU is the same in Shopify and Etsy.
If the product is not on Etsy, transfer it. See Transfer products between Etsy and Shopify.
For a bundle item, match or transfer that item, including every variation, in the same way.
If an ordinary product should not sync to Etsy, use tags to stop its stock from syncing. See Control Stock Syncing Using Product Tags. Tags do not stop this error for bundle items.
Still seeing it?
If the product is matched, the Etsy listing exists and the error comes back, contact support. Tell us the product name and when the error appeared.