Absolutely your best bet is to do as sons n daughters says and cancel the transaction.

I had a look at one of your items and I can see that you do exclude quite a lot of areas but maybe you need to expand that if you don't want any international sales at all. I think you'd be best to limit sales to Australia only, for sure, because postage overseas would really push up the cost, well beyond the price of many of the items.

I know you may be thinking that if there is some way to enable the postage for an overseas buyer that they are picking up the extra postage cost, not your problem, but it would be your problem if the buyer found a problem with the item and made an ebay claim. I think then that you'd find it wasn't worth your while to pay return postage and you'd be out of pocket. A lot. Some unscrupulous buyers might realise that. Not that I am saying the current buyer is like that.

But better to just cancel.

@trwar-7971 wrote:

Hello, I have sold an item but buyer cant pay because I have not enabled international postage. What can I do.

Thanks in advance

Go to the dropdown at the left of the sold item and select cancel. Then select the option of problem with buyer's address (or something to that effect). Then submit. The sale will be cancelled and you'll get your fees back that are charged at the time of sale. If you don't want to sell overseas, you need to block international buyers.

Edited to add: looking at your sold items, why are you selling at a loss? It doesn't make sense? A sale isn't just a sale, you have to be making a profit, but looking at your sold items, most of them you are losing money. Why would anyone sell at a loss?

Given the prices of your sold items, by the time you factor in postage for an international sale, you'd be taking a massive hit. Cancel.