Not had it checked at all this season, nor have I seen any other people have to do anything other than scan their tickets at the turnstile, apart from the first home game when they were checking Covid passes but had to sack it off as the queues were stretching back to the station bridge with...
To be honest I had no idea that this existed until my second visit to the Amex this season when, for whatever reason, the NFC (near field communication) on my Apple Wallet wasn't working. Luckily the steward was on hand to show me how to bring up the QR code.
When you open your ST on your phone there are three little dots in the bottom right hand corner which when pressed open up a QR code. This can be scanned under the reader in the same way that a print-at-home ticket is.
Get your neighbour to screenshot the QR code and send on.
*Technically, against the rules, but if your nephew is as enthusiastic and positive as most US sports fans then it’s all good.