Conditional copying in dynamic range

try

Option Explicit

Sub ISIN_Copy()
    On Error GoTo ErrorHandler
    
    Dim xlRng As Range
    Dim cellVal
    Dim fAddr$
    Dim i&, lngRowStart&
    
    lngRowStart = 2
    For Each cellVal In Range(Cells(2, 4), Cells(Cells(2, 4).End(xlDown).Row, 4)).Value
        Set xlRng = Columns(2).Find(What:="1", LookIn:=xlValues, lookat:=xlWhole, After:=Cells(lngRowStart, 2))
        If Not xlRng Is Nothing Then
            If fAddr = vbNullString Then
                fAddr = xlRng.Address
            ElseIf fAddr = xlRng.Address Then
                Exit For
            End If
            Range(Cells(lngRowStart, 3), Cells(xlRng.Row - 1, 3)).Value = cellVal
            lngRowStart = xlRng.Row
        Else
            Exit For
        End If
    Next cellVal
    Exit Sub
ErrorHandler:
    MsgBox Err.Number & ": " & Err.Description, vbOKOnly + vbCritical, "Error"
End Sub