See your sold items and see the auctions waiting to be paid for
If your auction had bidders - once it's ended, you'll be able to see the status of the auction.
If the buyer doesn't send the payment within 3 days, you can mark the auction as not paid. This will give a black mark to the buyer and prohibit them from bidding on any other items for 3 days. You should only do this if they have failed to reply to any messages and did not send any payment.
If your buyer does not submit payment, don't worry, you can just list your item for sale again!