Summary
Some product data, like price and availability, naturally changes over time. You need to maintain your product feed regularly to keep this information up-to-date.
You can use supplemental feeds and the Products API to update product data. Supplemental feeds can only be created in the Merchant Center UI, and they must be linked to a primary feed.
Manual steps
To maintain your inventory with supplemental feeds, see Create a supplemental feed.
You can also use automatic item updates to keep price and availability information up-to-date. Merchant Center can use embedded structured data from your website to update products if the price or availability differs from the information currently stored in the Merchant Center.
Automatic item updates are designed to fix small problems with product price and availability, not to be the main method of updating product data. You should use them in addition to supplemental feeds and the Content API.
To enable automatic item updates, follow the steps in About automatic item updates.
Automatic steps
To update information product information with the Content API for Shopping, use the Products API.
You can use the insert and update methods to create and update
individual items.
Like product inserts and updates, multiple inventory updates can be batched into
a single Content API for Shopping call using the products.custombatch method.