You can retrieve stock levels for a given site, which will return you the product id and stock level at that site.
Get stock levels
|Get stock levels at a given site
GET /v1/companies/5678/sites/234/inventory ?show_online=true
|Filter products by whether they are enabled for Online Products menu
id represents a product id.
show_online filter can be
true for enabled Online Products,
false for disabled Online Products, or no filter to return all products at the site.
List of Webhooks
Here is a list of the supported
When a product's stock runs out. You will receive a
stock level for that product.