How to get Item Available Quantity by Lot (Item Tracking Lines) with AL + how to check if a Lot No./Serial No. is valid

Hi,

please,

1) How to calculate the item available Quantity by Lot No. or by Serial No. with AL.

2) how to check if a Lot No./Serial No. is valid (already exists) with AL. (ex: how to check if LT10 is a valid Lot No. related to an item and a Location).

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Thanks in advance,