Sold something on ebay – received payment – went to the post office and sent it off. Just got email from buyer saying received but nil postage and had to pay handling fee. What’s happens next – I’ve still the original post office receipt?

how much are we taking about£?

Contact Royal Mail, sounds like the stamps etc have fallen off. With proof, they should refund the buyers money.

Maybe the post got wet (with all the snow etc.) and they did fall off. If you have the receipt it should be pretty easy to prove.