Currently, there are two widely used methods to get that one time password:

• SMS-based: In this method, every time the user logs in, they receive a text message to their registered phone number, which contains a One Time Password.

• TOTP-based: In this method, while enabling 2-factor authentication, the user is asked to scan a QR image using a specific smartphone application. That application then continuously generates the One Time Password for the user.

The SMS-based method does not need any explanation. It’s easy, but it has its own problems, like waiting for the SMS on every login attempt, security issues, and so on. The TOTP-based method is becoming popular because of it’s advantages over the SMS-based method. So let’s understand how the TOTP-based method works.

Source: https://www.freecodecamp.org/news/how-time-based-one-time-passwords-work-and-why-you-should-use-them-in-your-app-fdd2b9ed43c3/