Vlidating barcode scanner data entry in a text box, by If function

Hi all,
I have a userform, which is updated by a barcode reader.
When i want to validate one of these textboxes which has to have a fixed input, i can not use "else".
the code is as below,

Public Sub endtxtbx_Change()
    If endtxtbx.Value = "11EF" Then
            'some codes here
    End If
End Sub

i want to show a msgbox after else, something like,

Public Sub endtxtbx_Change()
    If endtxtbx.Value = "11EF" Then
            'some codes here
    else
        MsgBox "Invalid Input"
    End If
End Sub

but, when i do so, it'll only show the Msgbox by any changes.

Any Idea where is the problem, or what is the solution to do something like this?