You will also need to enable Basic Authentication on your scan server. Not sure why they are requiring Basic Authentication when it sends username/password in clear text to the Office 365 portal but they do. This is one feature that should be corrected ASAP.
Run the following command on your scan server to verify the Auth/Basic setting:
winrm get winrm/config/service
Run the following command on your scan server from an elevated prompt then reboot to set it:
winrm set winrm/config/service/auth @{Basic="true"}