you're supposed to enter the bar codes on stubhub not do a transfer which kind of sucks because barcodes are only released 48 hours before the game.
At Fenway I did that - tonight - because of the StubHub fails (can't sell tickets easily without a row number) -- but if you sell through StubHub, the transfer should go through automatically to the customer.
Outside of StubHub - in the App - there is a transfer tickets feature under Tickets.
Used it tonight because I couldn't sell mine on SH.