The author works at Kiwi.com, and says there are '70,000 times a day a customer clicks the Pay button on our platform' which is a little under 1 QPS.

Uber, by comparison:

'Trips during the quarter grew 21% YoY to 2.8 billion, or approximately 30 million trips per day on average.'

That would be about 350 payments per second if load was evenly distributed.