You can try out Nextiva vFax to solve this error. I have heard that https://cocofax.com/
will direct you to the information of PortServer TS - Fails to receive faxes if you need. Just log in to your Nextiva vFAX portal and verify that the fax was not received. In case the fax was received but you were unable to get a notification, just verify the sender comprises a 1 and area code when calling your Nextiva fax number. By dialing the 1 and area code is needed and makes sure the fax is received. Then call your Nextiva fax number and make sure it is gathering up with a fax tone. In case n not, please contact Nextiva Support and take two examples of the unsuccessful faxes and send to Nextiva Support within 24 hours from the time when the error started. Don’t forget to add, the sending and receiving fax number, the right time and time zone the fax was sent, and the issue if you can.