[RobMurray]

That wouldn't help, at least with my bank in the UK, the iframe just shows a message to open the mobile app to approve the payment. The payment details are then shown in the app, you don't interact with the page in the iframe at all.

[hn_throwaway_99]

But that would still require an eagle-eyed consumer, which (coming from experience working in the fintech space) is quite rare.. I.e., you may know the iframe is supposed to just ask you to open your mobile app, but I think the vast, vast majority of users wouldn't think twice if that iframe had been hijacked and instead asked them to enter their credit card information directly.