Earlier quoted context omitted.
TOTP not accepted? (When will people learn that biometrics are not another factor: they're entirely public and irrevocable. It's not just security theater, but Apple & Google know that this forces you into their ecosystem, which should be illegal. Of course, Brussels is full of rubes anyway.)
TOTP not accepted, because the confirmation for payment must include the amount to be paid, which cannot be done under TOTP as far as I know.
When confirming a large transfer, you also need to enter the payment amount in the device, and I assume this gets hashed into the number as well.
More recently (last 3/4 years), you can also use their mobile app to do this instead / as well as.