Incorrect phone line connection or a line sharing issue.
- Verify the telephone cable is firmly plugged into the printer's LINE port and the wall jack.
- Ensure no other device (phone, modem, answering machine) is sharing the line and off-hook.
- Disconnect all other devices from the phone line. Connect the printer directly to the wall jack.
- Listen for a dial tone on the printer's operation panel if available, or use a working phone to test the wall jack.
If that didn't work, the issue may be with the phone service itself (VoIP services often cause fax problems) or the fax number you are dialing is incorrect. Confirm you are dialing the full number, including any required prefix like '9' for an office line.
Heads up: Fax performance can be unreliable over internet-based (VoIP) phone lines. Use a traditional analog landline for best results.