From IraAPI logs of IraDialer server , retrieve the hangup event associated with call_uuid.
Refer to example below where failure_phrase, failure_status sent by the gateway(chime,twilio) indicate the reason for call initiation failure.
{
"event": "hangup",
"status": "OK",
"tenant_id": "tester_id",
"call_uuid": "3cf35665-14c0-4197-a2b4-00e0bae85a42",
"call_params": {
"AMDTreatment": "Disconnect",
"CampaignKey": "0",
"QId": "0",
"BeepDetection": "false",
"isCPAEnabled": "true",
"From": "null",
"To": "null",
"RP": "null",
"Queue": "null",
"Agent": "null",
"AgentUUID": "null",
"AgentConfID": "null"
},
"event_data": "NORMAL_TEMPORARY_FAILURE",
"failure_status": "400",
"failure_phrase": "To is not valid E.164",
"event_url": "xxxxxx",
"timestamp": "2022-03-21T11:58:55.571941Z"
}