Comm error 345 ? What does it mean?

Check phone line. use a normal phone and plug into the same phone wall socket that the MFP is using, do we have a dial tone? Do we have a noisy line, any buzz or crackel will cause issues if there is no dial tone ring line supplier, If it is noisy line do the same

Also check phone line is plug into "line" socket in the back of machine not "ext'

Also check no prefix is required to dial out, unit needs its own phone line..

Also try using resolution of fax as standard not fine, this requires less info to go threw the line