Royal Mail OBA - Proof of postage for lost item claim

Hi, could anyone tell what the correct procedure is for obtaining ‘proof of postage’ when sending items with my Royal Mail OBA / Click & Drop account. I would like to make a Royal Mail claim for a lost item.

So at the end of each day I bag up everything into the separate classes as required, add a bag label to each bag and then drop them off at the local post office with the manifest, ready for collection.

How do I obtain a proof of postage without having to get each individual parcel scanned? And do I need proof of postage to be able to claim if i’ve purchased the postage through my OBA account?

Any advice would be most appreciated.