When you log in for the first time, you are prompted to enable multifactor authentication. This method often includes receiving a code though a selected channel in order to validate your identity.

For more information, see Manage Multifactor Authentication.

The code is good only for 60 seconds. If you do not type that code on the CSP sign-in page and click Log In within 60 seconds, you have to get a new code and try again.