1. Google Merchant.The first step to list products on Google Shopping is to send a data feed to Google using the Google Merchant Center. Sometimes, you may need help troubleshooting your feed. Keep in mind not all the issues on Google’s merchant dashboard account page are errors which cause your products not displaying.

Critical Product errors result in products which won’t be displayed, while warnings or suggested optimizations are just suggestions to optimize your feed. To help you out with common errors, we’ve generated a list with the most common errors and how to solve theme.

Please remind that you can find the detailed information of the Google Shopping Feed right in your Google Merchant Center.

Source: https://support.google.com/merchants/answer/188494