Most banks now require their app for MFA for payments, sadly. They used to offer these "calculator" devices but most banks I know of in my country now require their app. Which sucks for me because I don't want to have my authenticator on a hackable internet-connected device.

and as soon as you login to their app once, that other key gets invalidated.

It took weeks to convince them to switch me back to that key because they couldn't understand the concept that their app refused to run on my phone

Yeah here they just sent an email "from <date> onwards all verificators are revoked, from now on you must use the app" :(