Google Shopping Feed App helps you add promotion IDs which will help your products perform better
Adding promotions to your products will increase your product score. This will ensure that your products are better served in Google shopping ads.
In order to opt for promotions, you have to enter the Google Merchant center promotion program. After you get approval from Google you can create promotions. You can then create promotion based on the amount, percentage, free gifts, or free shipping. You can then add these promotions either to your selected products or your complete feed.