This error occurs when the SKU, or the a SKU in the product group you are trying to list to eBay, is missing a primary image URL. People love to see what a product looks like before purchasing it - don't deprive them of this!
Please note that for eBay, we push data for the entire product group to eBay when at least one SKU within the group is set to list. This is because eBay needs all variation information for a group when creating the listing. Therefore, it may be a SKU in the product that's not even set to "List" to eBay that is causing the error to occur.
It's easy to add images in Zentail! To learn how, check out Image Management on Zentail.
Images must be LESS THAN 24MB in size
It must have a minimum of 1000 pixels
Images must NOT have password protected links.
If you use Dropbox, see this FAQ to generate sharable links: Creating Public Links