It is mandatory at Catch that the product must have UPC. You are getting this error because the Barcode field
on Shopify for the Product has been set as blank
Kindly update the Barcode field on Shopify and then publish the product from the App
Your product will be published to Catch.
Note : In case you do not have UPC for the products and want to publish them without UPC then you need to contact Catch once to allow you to list product without barcode.