404% is the average number of SIP 404 Responses compared to all call attempts.
404% = (sum of 404 release cause codes from CDRs) / (sum of attempts) * 100
A SIP 404 Not Found response indicates the server has definitive information that the user does not exist at the domain specified in the Request-URI. This status is also returned if the domain in the Request-URI does not match any of the domains handled by the recipient of the request.