The most common reason is that no stock management is active for the product. In most cases, this will usually be required.
However, there are products where this is not necessary, such as a deposit item.
Stock management can be adjusted for the desired product under the “Availability” tab.
Open the relevant branch (in most cases, there will only be one) and on the “Optimal Stock” tab, adjust the “Stock Management” option.
Another reason why the stock of a product cannot be adjusted is when the product is configured as a related product of type “Revenue on related products”.
This can be checked under the “Related” tab of the product.
