Problem with DAX Formula

Hi mark_endicott , before of all Thanks for the support, I've changed the tables references and created the calculated column but it gives me an error that I don't understand:

A table of multiple values was specified when a single value was expected.

The lookuptable is a historic recording of price changes of products and in the same date can be multiple product price changes.
The base table is a document tables with purchase and selling values(that i filter in Power Bi).

Here is a screenshot:

Only for yolur information the BaseTable Date can be retrieved from another table related to basetable.

Here is the code adapted to my work:

Purchase Price = 
VAR _date = documentidettaglio[DataProtocollo]
VAR _prod_code = documentidettaglio[ArticoloEtichetta]
VAR prev_date_table =
    CALCULATETABLE (
        ADDCOLUMNS ( Storico_Test_1, "max_date", MAX ( Storico_Test_1[Data] ) ),
        Storico_Test_1[Data] < _date,
        Storico_Test_1[ArticoloEtichetta] = _prod_code
    )
VAR prev_date =
    MAXX ( prev_date_table, [max_date] )
VAR look_up =
    LOOKUPVALUE (
        Storico_Test_1[Acquisto Netto],
        Storico_Test_1[ArticoloEtichetta], documentidettaglio[ArticoloEtichetta],
        Storico_Test_1[Data], documentidettaglio[DataProtocollo]
    )
RETURN
    IF (
        ISBLANK ( look_up ),
        CALCULATE (
            MAX ( Storico_Test_1[Acquisto Netto] ),
            Storico_Test_1[ArticoloEtichetta] = _prod_code
                && Storico_Test_1[Data] = prev_date
        ),
        look_up
    )

Thanks in advance for all your support