Make sure:
If you have set up authentication by SMS or voice, when you attempt to sign on to your Mac machine, you will receive a passcode with which to authenticate.
  • Voice call: you will receive a phone call with an automated recording of your passcode.
  • SMS: you will receive an SMS with details of your passcode.
  1. Sign on to your Mac machine.
    You'll see the Authenticating window. You'll receive an SMS or voice message to your mobile device, showing the one-time passcode.

    Screenshot of the Authentication window showing the passcode field.

    If you didn't receive a passcode by SMS or voice call, click Resend Passcode.

  2. In the Authenticating window, enter the passcode and click Sign On.

    You'll see the green checkmark indicating authentication is successful, and you're signed on to your Mac machine.

    A screen capture of the Mac login desktop following successful sign on.