To configure the Microsoft Authenticator app, you will need both a smartphone and another device, such as a computer or tablet.
You will receive a message on your computer noting the registration of the app was successful.
Every time you sign into your Key Account, you will get an additional security verification prompt displaying a random number on your computer screen similar to the one below.
On your phone, tap the notification to open the Microsoft Authenticator App and enter the same number shown on the computer.
If you cannot use the app at that time for some reason, the security verification prompt provides an "I cannot use my Authenticator app right now" option, which allows you to use a different method to verify your identity and access your account.
Click on that option, and you will get a list of alternative ways to verify your identity, such as a text or a phone call. Pick any of the methods and follow the prompts.