problem vba code for multiselect listbox (userform)

in the attached file, I drafted a userform "PANDL" (which is actually the copy of the page 2 of the userform "cargo2016").

In this userform I would have like to be able to select several ref and to populate the userform with infos for each of them..

But my knowledge in VBA is null and I don't know how to say for each selected item in the listbox "REF", get datas.....

I tried to put a "ok" command to validate the selection in REF listbox with following code...

Private Sub cmdOkay_Click()
Dim i As Long, msg As String, Check As String

'Generate a list of the selected items

    For i = 0 To Me.REF.ListCount - 1
        If Me.REF.Selected(i) Then
        GetData
        End If
    Next i


If msg = vbNullString Then
    'If nothing was selected, tell user and let them try again
    MsgBox "Nothing was selected!  Please make a selection!"
    Exit Sub
Else
    'Ask the user if they are happy with their selection(s)
    Check = MsgBox("You selected:" & vbNewLine & msg & vbNewLine & _
        "Are you happy with your selections?", _
        vbYesNo + vbInformation, "Please confirm")
End If

If Check = vbYes Then
    GetData
Else
    'User wants to try again, so clear listbox selections and
    'return user to the userform
    For i = 0 To REF.ListCount - 1
        REF.Selected(i) = False
    Next
End If
     
End Sub

but obviously the ref.value remain "null".....

can someone give me some tips to search further?