Configure OTP Notifications for MFA
To use one time passwords (OTPs) as an authentication factor, users need an Authenticator app such as:
Authy (Google Play / App Store).
Google Authenticator (Google Play / App Store).
Auth0 Guardian (Google Play / App Store).
Microsoft Authenticator (Google Play / App Store)

Upon signup, they can scan a code and set up the app, upon which it will begin generating one-time codes. Afterward, when logging in to the app, the user can simply check the authenticator app for the current one-time code:

Your user enters the code at the prompt:

Your users will need to have an OTP Authenticator app installed on their mobile devices.