(I realise you parcel was picked up after a few days.)
In terms of the original question, then according to the poster of msg #9 in this thread, it may not be that simple. https://community.ebay.co.uk/t5/Seller-Central/Royal-Mail-have-lost-the-Simple-Delivery-parcel-I-sen...
(The thread was started by a different person to msg #9.)

That member says they've been told by ebay customer services that handing over (and scanning) an item at a post office does not count as "scanned into the courier’s delivery network" for Royal Mail.

I've no way of verifying who said what, nor whether there is any other factor which affected eBay's decision.