Etsy turned the product away because the shipping profile Shuttle sent with it is not one Etsy accepts for your shop. The product was not created on Etsy.
Why it happens
When Shuttle transfers a new product to Etsy, it picks a shipping profile for it: the Etsy profile matched to the product's Shopify shipping profile, or your Etsy default when no match applies. Etsy rejects the product when that profile is no longer valid. Check for these:
The profile was deleted or replaced in Etsy. Shuttle still holds the old list, so your default or a matched row points at a profile Etsy no longer has.
The default was saved against an old list. The Shipping Profiles page was open before your Etsy profiles changed, and the saved default no longer exists.
Only new transfers are affected. Updates to products already on Etsy do not send a shipping profile.
How to fix it
In Shuttle, go to Settings → Catalog Mapping → Shipping Profiles.
Under Match shipping profiles, click Refresh. Shuttle reloads your Etsy profiles and removes any matched rows that point at profiles Etsy no longer has.
Under Default shipping profiles, pick your Etsy default again from the refreshed list.
Re-match any Shopify profile whose row was removed.
Click Save.
Transfer the product again.
If Shuttle tells you your Shopify store moved to market-driven shipping, the mapping lives on the Shipping → Collections page instead.
For how matching and defaults work, see Ensuring Products Are Assigned the Correct Shipping Profiles.
Still seeing it?
If the transfer fails again after you refreshed the profiles and chose a fresh default, contact Shuttle support with the product name and the Etsy default you selected.