Hello there,
We are using an API feed for our google merchant account.
the feed works properly and contains all of the fields we need (brand, SKU, price, sale price, photo url, product url, etc..).
However, there is one field that is missing and it is the [sale_price_effective_date] which is vital for us in order to have our products shown on google shopping with the sale badge.
We either need to set up a new feed or add a secondary feed that completes the main API feed we have but that has the [sale_price_effective_date] field.
The sale price effective date, is not required to be eligible for the sales badge.
The purpose of the effective date is to start and stop and specific dates.
This is used if you believe the data when changed does not get updated quick enough, this is when using the effective date will resolve that issue. Considering content API updates as soon as you change something, this field would not be necessary to stop and start the sale.
However if you want to add it, you can do so using a supplement feed: https://support.google.com/merchants/answer/7439058?hl=en