In order to export listings from Shopify to Etsy you need to set your default Etsy Shipping profile to Fix on Etsy .
In case you are using calculated Shipping as your default shipping profile please change it to "Fix" shipping profile.
To view the error please go to shopUpz app :
Click on "Export listings" tab
Click on "Sync History" tab
Hover the error message and the following error message will be displayed (View image below
In order to resolve the issue - please go to your Etsy shop manager and change your Etsy Shipping profile to "Fix"