This error is cause by using inventory management on Shopify & allowing out-of-stock products to be sold
This error sometimes pops up when shops use variants and inventory management on Shopify, e.g. when you allow products with zero inventory to be sold anyway. We apply the following rules on a variant basis to set the availability tag that Facebook expects.
- if inventory_quantity > 0 => availability = in stock
- OR if inventory_policy = continue => availability = in stock
- OR if inventory_management = not set => in stock