Hello,
Whenever you sell an Item with a Serial Number, you can have it added to the Known Serial Number register. This will happen when the Invoice is approved. This feature is optional: if you want to use it, switch on the Update Known Serial Number Register option in the Stock Settings setting.
You can, also create the invoice from the delivery. In this case there should be two rows on the invoice and the known serial number register will be updated accordingly.
Brgds
Rasmus