One-Time PIN Mobile App Feature One-Time PIN is a free new mobile app feature providing iPhone and Android users with an alternative to the SMS OTP option. The One-Time PIN mobile app feature locks your device to your account and once you have registered, you will never be asked for an OTP when banking through the app. This feature also allows you to generate an offline OTP for use when banking online. To download the Citibank Mobile App, Simply visit the App Store or Google PlayTM store on your iPhone or Android and search for "Citibank AU".