Need help with DAX Formula

Hi ahmer_malick ,

Thanks for the update and additional details.

Please try the below updated measure, which evaluates the last available Promise Date per Branch Plant and SKU within each month and returns the corresponding Quantity Available value:

Qty Available Last Actual Day In Month =
VAR _SelEOM = MAX ( 'Calendar'[EOM] )
VAR _LastDateInMonth =
    CALCULATE (
        MAX ( 'Sheet1'[Promise Date] ),
        ALLEXCEPT ( 'Sheet1', 'Sheet1'[Branch/ Plant], 'Sheet1'[Parent 2nd Item Number] ),
        'Sheet1'[Promise Date] <= _SelEOM,
        'Sheet1'[Promise Date] > EOMONTH ( _SelEOM, -1 )
    )
RETURN
CALCULATE (
    SUM ( 'Sheet1'[Quantity Available] ),
    FILTER (
        ALLEXCEPT ( 'Sheet1', 'Sheet1'[Branch/ Plant], 'Sheet1'[Parent 2nd Item Number] ),
        'Sheet1'[Promise Date] = _LastDateInMonth
    )
)

 Please let us know if it gives the expected output for all SKUs across branches.

Thank you.