Outbound Fax Busy Call Status

We are trying to send a fax to a phone number with a fax machine that rings 5 times (about 30 seconds) before accepting the call as a fax. The RingCentral call log shows all these fax call results as 'Busy' with a call Length around 31 seconds. Why does RingCentral result these calls as busy? Is there a setting that sets the call as busy if it rings more than 30 seconds? A regular stand-alone fax machine sends to this fax machine just fine, just having problem with RingCentral.