Fax Reception issue in Konica Minolta C421

Dear All

I am facing Fax Reception problem in Konica Minolta BizHub C421
I can send fax but couldn't receive any fax.
If I connected the fax line to a dedicated simple fax machine there is no issue in fax TX or RX.
But when the fax line connected to the C421, fax Rx is not happening.
Please suggest any setting to be done in service mode . Machine location is in UAE

Best regards

Gopa