What does this error mean?
Etsy did not create the listing because one of the details it requires reached Etsy with no value. Nothing was added to your Etsy shop. Transfer History shows this error but does not say which field was empty. When you transfer a single product from Products, that product's row can show Etsy's own message, which names the field.
Why is this error usually a one-off?
Shuttle fills in Etsy's required details before it sends a product, so a blank field on your Shopify product does not normally reach Etsy empty:
Description: a product with no description is sent with a short placeholder description.
Price: a product with no price, or a price below Etsy's minimum of roughly $0.20 USD, is raised to that minimum.
Quantity: a product with no stock number in Shopify gets your default stock quantity, and the quantity sent is never zero.
Because of this, the error rarely comes back when you try the same product again.
How do I fix an empty required field error?
Go to Products, open the Shopify → Etsy tab, find the product and transfer it again.
If the transfer fails with the same error a second time, contact Shuttle support and include the product name.