Under the listing or sale in your StubHub account, click “Enter barcodes” and enter the numeric barcode that’s printed on the ticket.
After you’ve entered your barcodes on the StubHub listing/sale, you're done! The tickets will be delivered electronically to your buyer, each with new barcodes - which means yours wont be valid anymore.
You won't need to post your paper tickets to your buyer since they'll be sent electronically.
It's a good idea to hold onto your tickets - if an event is cancelled, you may need them to claim a refund.