We don't do airport standby, and if so there would be no extra payment. By regulation airport standby is flight duty if called out and simply duty if not.
We have however home standby, up to 16 hours, the total of home standby and the resultant flight duty is capped at 22 hours, excluding the hours until 9AM if not called before that. Response time is one hour. And of course no extra payment either, however our base pay makes up for around 80% of our total pay.