Fix Shopify False Out-of-Stock Error

Every item in my Shopify store suddenly shows as “out of stock” whenever a customer clicks Add to Cart or Buy Now, even though the inventory levels are correct in the admin. I have not installed any new apps, touched the code, or updated the theme recently, and I am not using any third-party inventory services. The problem affects every single product, so it is blocking all sales. I need someone who knows Shopify’s inventory logic inside out to locate the source of this bug and restore normal Add-to-Cart and checkout behaviour right away. Acceptance criteria: • Root cause documented and resolved without breaking the live theme. • All products can be added to the cart and purchased without the stock error. • Fix verified in an incognito session and on at least two different browsers. Please be prepared to start immediately and work on the live store (I will provide collaborator access).