Way back in Dec 2017, Shopify change the json filter so it stopped outputting the inventory_quantity and inventory_policy. This change also affected the *.json endpoints on the front end, such as [website-domain]/products/[handle].json?variant=12345.
Is there a way to enable this feature on older stores?
You need to contact Shopify support and tell them the following:
Please ask the Technical Team to disable the inventory_policy and inventory_quantity on json filters on the back end.
The Technical Team has a internal document to resolve this. Don’t let support try to side track the conversation if you want a speedy resolution, push them to contact the Technical Team.
WARNING: If you enable this feature, the json properties inventory_policy and inventory_quantity will no longer be included for products or variants when you use the json filter, or json endpoints of your storefront, such as /products/handle.json