Etsy turned down the new listing because it did not accept the shipping profile Shuttle sent with it.
Why it happens
A profile was deleted or replaced on Etsy. Shuttle still had the old profile saved as your Etsy default or in one of your matching rows. When this happens, Shuttle reloads your Etsy shipping profiles and tries once more, using your Etsy default if the old profile is gone. You only see this error when that second try also fails.
A profile mapped to a Shopify collection is no longer on Etsy. This only applies if your Shopify store uses market-driven shipping. In that case Shuttle picks the profile from your collection mapping.
How to fix it
In Etsy, check that the shipping profile you want to use exists in your shop.
In Shuttle, go to Settings > Catalog Mapping > Shipping Profiles.
In the Match shipping profiles card, click Refresh to load your current Etsy profiles.
Under Default shipping profiles, choose a profile in Etsy default.
In the matching table, check that each row uses a profile that still exists. Choose a new one for any row that does not.
Click Save, then transfer the product again.
If the page shows a banner saying your Shopify store moved to market-driven shipping, follow these steps instead:
Go to Settings > Catalog Mapping > Shipping → Collections.
In the Map Etsy shipping profiles to Shopify collections card, click Refresh.
Under Default shipping, choose a profile in Etsy default, and check each mapping row.
Click Save, then transfer the product again.
Still seeing it?
Contact support if the error comes back after you refreshed your profiles, chose one from the list and transferred the product again. Tell us which product failed and which shipping profile it should use.