For information: some books sent to people in Brazil (some as far back as October 2019) are being returned to me (2 months after being sent!) because they need an S10 label. Nobody knew what it was at the French post office but it turns out to be a CN23 custom label with a barcode (I was told to use a CN22 without barcode but the regulation changed during 2019). So I am resending the books to Brazilian customers. Thank you for your huge patience!