Tag Shopify products that are on sale
You can use Auto Tags to tag products in Shopify if any of the variants has a "price" lower than the "compare price", then add tag SALE. The app will take care of removing the tag if none of the variants has a price lower than compare price.
You can configure it under Sync Product Tags Based On Attributes when creating workflow of Product type.
Here's the screenshot of how to configure the above workflow in the app: