How to Add a String to the beginning of every value in a range

Try this.

Public Sub Concatenate Test
Dim invoiceNameRng As Range
Dim invoiceNameValue As Range

    Set invoiceNameRng = ThisWorkbook.Worksheets("Sheet 1").Range("B2", Range("B2").End(xlDown))

    For Each invoiceNameValue In invoiceNameRng
        If invoiceNameValue.Value <>"" Then
            invoiceNameValue.Value = "E-" & invoiceNameValue.Value
        End If
    Next

End Sub