Etsy refused to create the listing because one of its text fields is longer than Etsy accepts.
Why it happens
This error appears when you transfer a product from Shopify to Etsy. The message shown with the error names the field Etsy refused.
The title and tags are not the cause. Shuttle already shortens titles and leaves out tags that are too long, and a title that is too long shows a different error. So check the description first. The description Etsy receives is built from:
The product's description in Shopify.
The product's translation instead, when Transfer to Etsy in (Settings → Products → General, under Shop languages) is set to a language other than your store's main language.
Any text Shuttle adds to it from Add above description, Add below description and Content from metafields.
How to fix it
Read the field named in the error message. If it is not the description, see "Still seeing it?" below.
In Shopify, open the product and shorten its description. If Transfer to Etsy in is set to another language, shorten the product's translation for that language.
In Shuttle, go to Settings → Products and open the Shopify → Etsy page. In the Product Description section, shorten the text in Add above description and Add below description, and remove any Content from metafields source that adds long text.
If you want to send only part of long descriptions, choose an option under Truncation method in the same section, such as Keep first 2 paragraphs.
Click Save, then transfer the product again.
Still seeing it?
Contact support if the error names a field other than the description, or if it still appears after you have shortened the description and the text Shuttle adds to it. Tell us which product it is and copy the full error message.