Who is responsible for postage when a label is purchased on eBay?

I only use Royal Mail as I will not, under any circumstances use Evri, and I have always been impressed with their service, always used tracked 48 and the vast majority arrive within 2 working days with the odd occasion of taking 3 days.

I recently sold a small thin paperback book and here is the exact sequence of events and please note that this was custom postage NOT simple delivery as it was £3.99, large letter and under 100 grms.

Sold the item and buyer paid immediately.

Packed and weighed the item in a padded envelope - 78 grms.

Went to 'awaiting dispatch, and clicked on 'get postage label.

Selected large letter and then selected' up to 100 grms

Printed the label and taped it to the envelope

Next morning, took it to the post office along with several other parcels and they were scanned into the system.

Happy days - job done or so I thought.

A week later, customer reports item not received so I checked the tracking, as follows

Item accepted at Parcelshop

2 days later 'Your item has reached Jubilee MC

It has never moved since.

I got the customer to check the tracking to confirm and refunded in full immediately.

I decided to put in a claim with Royal Mail so I filled in the online claim form and got confirmation of the claim.

3 weeks later heard nothing so I spent nearly 20 minutes on the phone to eventually get through to customer services

They looked up the claim and said that as I had purchased the label through eBay, it was eBays responsibility.

I explained that it was NOT simple delivery and they said if is says on the label 'Paid and printed from eBay' then it is eBays responsibility

eBay CS says it is Royal Mails responsibility, Royal Mail CS says it is eBay's responsibility.

Institutional robbery and corruption - almost as bad as the Government!

Needless to say, it was such a small amount, I wish I hadn't bothered but it begs the question.......

Who is responsible for the postage?