All availability is based on documents. If, for example, we want a product to have 20 pieces in our warehouse, we need to create an entry document, for example a 20 piece consignment note.
We also have the ability to set it on the inventory->details tab in the availability field. If it is inactive, we turn it on in the settings:
In this way each time we create an item in the inventory, and we have changed its availability, a line with the corresponding item is automatically created in the document with the number ‘0’. The document line ID can be found in the settings->Purhases/Sales->Documents: