Hi avr, Duo Mobile can function as a passcode generator for third-party apps or provide additional authentication options for Duo-protected applications. Learn more about the differences here: https://help.duo.com/s/article/2242
It sounds like you are trying to use it as a passcode generator. To associate Duo Mobile with a third-party app, you will need to follow the specific instructions for adding a 2FA app for that service. Typically this involves navigating to your account security settings and following the instructions there. For an example, here is the process for Amazon: https://www.amazon.com/gp/help/customer/display.html?nodeId=201962420
