First, tell the staff you will use the o2 code. Otherwise sometimes they sometimes cancel the transaction. Then use Nero app and scan it. Then use o2 code.
I show the loyalty card first as I think doing the o2 voucher finishes the transaction. It might be possible the other way round, but I've not tried it.
I have a spare one if anyone needs. Must be used within 15 mins of getting the code so if anyone wants it and is near an Caffè Nero let me know
Just come back from Nero.