By default, the stockable products will not be allowed to have a
negative stock. If you want to make some exceptions for some products,
product categories or locations, you can activate the option *Allow
Negative Stock*:

For products:

1.  Go to *Inventory / Master Data / Products* and in the tab *General
    Information* activate this option.

For product categories:

1.  Go to *Inventory / Configuration / Products / Product Categories*
    and activate this option.

For individual locations:

1.  Go to *Inventory / Configuration / Settings* and activate the option
    *Storage Locations*.
2.  Go to *Inventory / Configuration / Warehouse Management / Locations*
    and activate the option the option *Allow Negative Stock* for the
    locations you choose.