Using One Time Code for MFA:

• When an MFA is challenged and doesn’t have an opportunity to approve through the Microsoft Authenticator Notification, a rolling one-time code can be used to do the secure login.
• This code can be obtained from Microsoft Authenticator App even in cases of poor or no network coverage.
• Click on I can’t use Microsoft Authenticator app right now when MFA is challenged
  
• Choose the second option as highlighted

• Then navigate to Microsoft Authenticator App on the mobile, select the account.

• Enter the One-time Code from here to the sign in page