HP LaserJet Pro 400 MFP M425 - Manual (Page 117)

5. Verify that the telephone service supports analog fax.
● If using ISDN or digital PBX, contact your service provider for information about configuring to an
analog fax line.
● If using a VoIP service, change the Fax Speed setting to Slow(V.29) or disable Fast(V.34) from the
control panel. Ask if your service provider supports fax and for the recommended fax modem
speed. Some companies might require an adapter.
● If using a DSL service, ensure that a filter is included on the phone line connection to the product.
Contact the DSL service provider or purchase a DSL filter if you do not have one. If a DSL filter is
installed, try another since these filters can be defective.
6. If the error persists, find more detailed problem-solving solutions in the sections that follow this one.
ENWW Solve fax problems 101