Presumably it's the pram that you had listed as pickup only. Why would you let the highest bidder dictate to you how to send it to them ?  I'd imagine your best course of action would be to cancel the sale using "problem with buyers address" and offer it to the second highest bidder.

https://www.ebay.com.au/help/selling/getting-paid/sellers-can-cancel-order?id=4136

Also read up on selling for the first time.

https://www.ebay.com.au/help/selling/selling/start-selling-ebay?id=4081