A bar with hints in the written function VBA

Question

1. I wrote a function in VBA:

Function LHV_v(T, compounds As Range, concentrations As Range) As Double
        Dim arr() As Variant

        Dim i As Long, j As Long, k As Long
        Dim curRow As Range
        Dim ret As Double, x As Double
        ReDim arr(2, 4)
        arr(0, 0) = "CH4"
        arr(0, 1) = 35.818
        arr(0, 2) = 35.808
        arr(1, 0) = "C2H6"
        arr(1, 1) = 63.76
        arr(1, 2) = 63.74
        arr(2, 0) = "C3H8"
        arr(2, 1) = 91.18
        arr(2, 2) = 91.15
        
        If compounds.Rows.Count <> concentrations.Rows.Count Then
            MsgBox ("Ranges differ in number of rows")
            LHV_v = 0
            Exit Function
        End If
        ' Loop through user input rows:
        k = 1
        For Each curRow In compounds
            arraycompound = Trim(UCase(curRow.Value2))
            For i = 0 To UBound(arr, 1)
                If arr(i, 0) = arraycompound Then
                    ' x retrieves user's input of concentration:
                    x = concentrations.Cells(k, 1).Value2
                    If T = 0 Then
                        ret = ret + arr(i, j + 1) * x
                    Else
                        ret = ret + arr(i, j + 2) * x
                    End If
                    Exit For
                End If
            Next
            k = k + 1
       Next
       LHV_v = ret
    End Function

which is called as follows::

=LHV_v(25;A19:A23;B19:B23)

2. While I'm typing in the formula bar, no hint window pops up (what to type in the function), as is the case with built-in functions, for example:

=SUM([...]

3. How to activate this option for functions created in VBA?