I'm confused by your last statement re. Signature on Delivery. What do you mean the barcode is void? Why would the barcode change if it's already manifested one for you?

The post office computer system refused to accept the already manifested barcode when Signature on Delivery was specified as an option. The only way then to send with SOD was for the lady to add a separate barcoded sticker for it over the top of my pre-prepared label's barcode (so that the non-working barcode would not cause problems along the way).

So this renders the whole C&S preparation I did pointless and actually ends up being more work for both me and the post office. I had to go back and notify the purchaser of the new barcode, and then also lose the benefit of any email notifications myself and the purchaser were subscribed to.

Don't worry, we were both as confused as you are and I'd love to hear if anyone else manages to get it to work for them.