Hmmm, can't help to complain OCBC's logic. (OCBC: A bank in Singapore)

They have a thing called OneToken, something like passkey but for OCBC only and without cloud sync. So each time you reinstalled the app, you can login and set up a lite version of OneToken, but to fully activate it, you have to get a 6 digits code from the letter they sent you.

With the limited OneToken, you can't change the mailing address. But to receive the letter, I have to update the mailing address.

Look, a loop born!