VBA - Index SumProduct with mis - vba

Question

I am new to VBA and am working on a userform at the moment that has 3 ComboBoxes that a user picks 1 item from each. The intent is for the code to look up the corresponding 4th value from the spreadsheet and return it to a textbox on the userform. Right now I'm getting a "Type Mismatch (Error 13):"
I have been fiddling with this for going on 3 days now. Some websites say the SumProduct function doesn't work in VBA, some say it does as long as you specify "WorkSheetFunction", and still some say you should instead use 'evaluate'.
Like in this post:
SUMPRODUCT Formula in VBA
(I didn't have much luck using 'evaluate' but my syntax might have been off)
Anyway, I created a quick example to show what I am trying to do. If anyone can help it would be tremendously appreciated.
worksheetdata
this is the code I have been trying:
Private Sub TestButton_Click()
textboxTesting.Text = Application.WorkSheetFucntion.Index(Range("Thickness"), _
Application.WorkSheetFucntion.SumProduct((Range("Wood") = "Oak") _
* (Range("Metal") = "Copper") * (Range("Box") = "Red")), 0)
End Sub

Answer 1

A better approach is to write your own function, I believe the below is much more understandable:
Sub Test()
Dim thickness
thickness = FindThickness("oak", "copper", "red")
MsgBox (thickness)
End Sub
Function FindThickness(wood As String, metal As String, box As String) As String
Dim rng As Range
Set rng = Range("Wood")
For Each cell In rng
If cell.Value = wood _
And cell.Offset(0, 1).Value = metal _
And cell.Offset(0, 3).Value = box Then
FindThickness = cell.Offset(0, 2).Value
Exit Function
End If
Next cell
End Function