Google Merchant disapproved my products due to the "Incorrect Value [Identifier exists]" error. What should I do?

Google Merchant disapproved my products due to the "Incorrect Value [Identifier exists]" error. What should I do?

Google Merchant disapproves products either because they don't have GTIN at all or if the value is incorrect. Here is a useful article from Google explaining possible reasons in detail.

GTIN is not a default Magento attribute, therefore, if you'd like to add it, go to Stores → Attributes → Product, create a new attribute, and enable the Use for Promo Rule Conditions setting for it to appear among the feed's attributes.


     
After making the changes, save the attribute and clear the cache to apply them. As a result, the attribute is now available in the list of attributes in any feed.