Etsy turned down the new listing because the shipping profile Shuttle sent is no longer in your Etsy shop.
Why it happens
Every new Etsy listing needs a shipping profile. Shuttle uses the Etsy profile you matched to the product's Shopify shipping profile. If your store uses market-driven shipping, it uses the profile matched to the product's collection. If there is no match, Shuttle uses your Etsy default.
A profile was deleted or replaced in Etsy. Shuttle keeps a list of your Etsy profiles from its last refresh, so it can still pick a profile that Etsy has removed. Check that the profiles in your Shuttle settings still exist in your Etsy shop.
How to fix it
Go to Settings → Catalog Mapping → Shipping Profiles.
In Match shipping profiles, click Refresh. Shuttle reloads your Etsy profiles and removes any match to a profile that no longer exists.
Under Default shipping profiles, make sure Etsy default shows the profile you want.
Check the mapping table. A Shopify profile that was matched to the deleted Etsy profile now uses the Etsy default. To match it again, pair it with a current Etsy profile in one row. If each row shows a Shopify profile, pick the Etsy profile on that row. If each row shows an Etsy profile, find the Etsy profile you want and pick the Shopify profile next to it.
Click Save.
Transfer the product again.
If your store uses market-driven shipping, go to Settings → Catalog Mapping → Shipping → Collections instead. Click Refresh and check Etsy default. Each row there is one Etsy profile. If a collection was mapped to a deleted profile, its row is gone, so pick that collection on the row of a current Etsy profile. Then click Save and transfer again.
Still seeing it?
Contact support if the error comes back after a refresh and the profile is still listed in your Etsy shop. Tell us the product name.