Try one or more of the following:
From the home screen, touch Settings > Fax.
In the Fax Mode menu, select Analog.
You may have problems with your phone line.
Are your fax messages not going through? Make sure that your printer is connected to a working analog telephone service.
Here are troubleshooting steps when unable to 'Send' a fax with Laser Multifunction Printers (MFPs).