There are item specifics requirements for each category in eBay. Sellers who are exporting from other marketplaces like Etsy and Shopify often doesn't have the required item specifics which is why the export is failing.
What are item specifics?
Item specifics are descriptive keywords that tell a buyer about your item. They may include brand, size, length, width, height, type, color or style and many more, and vary depending on what you are selling.
The required item specifics depend on the category your product belongs to. For example, the "Drums" category requires the "Type" item specific.
How to know if there are item specifics missing?
If there are item specifics missing, the product will not export and an error message will show under the Status column on the listings table.
As shown above, the error message will let you know which item specifics are missing.
Another way to check if there are missing item specifics is to open the Listing Editor.
From there, navigate to the Product Details tab.
You will see the required item specifics below.
This technique is suggested if you need to add item specifics to a particular product without necessarily creating a rule that will apply to multiple items at once.
How to use rules to automatically fill item specifics upon export?
Once you determine what items specifics are missing, you are ready to create automated rules that will add them for the relevant products.
From the Products page, click Rules.
On the right panel under Appearance, choose Item Specifics. After that, click on New Rule.
Under Action, click the drop down arrow and choose Add item specifics.
In the Name box (the left one), type the name of the item specific that is missing (i.e. color), then add the appropriate value (i.e. yellow) in the value box. Click Next.
Under Choose Products, you can enable Use Filters so that the rule will only apply if the specified conditions are met. Example, you may want the rule to only apply to a particular SKU, category name, brand, etc. If so, create the appropriate filters.
Alternatively, you can disable Use Filters and the rule will attempt to apply on all the products that are exported to eBay.
When you are done, make sure to click Create Rule then Save Changes at the bottom.
After the rule is created, you can export the items again or if you have Auto-Export enabled just wait for the next sync.
If you want to learn more about rules and filters, read this article.