The claim was transaction not authorize.
Then there are two ways you might still be able to resolve this.
If you have a receipt for the postage (either from the post office or from eBay, PayPal or another shipping service), call paypal and explain that this should be covered under Seller Protection. It does not matter that the tracking is expired; for Unauthorized you just need proof that it was shipped.
Otherwise, contact the buyer directly. Many Unauthorized Payment disputes aren't scams; they are the result of consumers receiving notices from their bank that their account may have been compromised. The bank then asks the consumer to challenge any unrecognized transactions. That challenge goes to paypal as a Retrieval Request (or "soft chargeback"), and is typically resolved by the seller providing proof of shipping, or by the buyer cancelling the chargeback when he remembers the transaction to be legitimate.
Good luck...
