"We detected an unusual sign-in attempt. To ensure that someone else isn't trying to access your account, your organization needs you to sign in using your corporate mobile device (the phone or tablet you normally use to access your corporate account). If you don't have your corporate mobile device with you right now, try again later when you have your corporate mobile device with you. If you continue to have problems signing in, contact your administrator."
- Login to Google Admin: https://admin.google.com/
- Go to Users >> Open the user account
- Go to "Login challenge."
- Click on "Turn off for 10 mins."
- Try to login again, and it should be fine