Diagnosing disconnection reasons
Find the reason in the table below, then follow the fix. For deeper diagnosis of specific cases:not_connectedoutbound calls (dial_failed,invalid_destination, spam blocks, and other SIP failures) — see debug outbound connection issues.- SIP-level signaling and media — inspect the call’s PCAP file, covered in debug SIP calls using PCAP files.
When a phone number makes many short calls in a short period, carriers might mark it as spam. The number then gets blocked and shows up as
dial_failed.| Disconnection reason | Call status | Description |
|---|---|---|
user_hangup | ended | Expected behavior, user hung up the call. |
agent_hangup | ended | Expected behavior, agent hung up the call. |
call_transfer | ended | Expected behavior, agent transferred the call. |
transfer_bridged | ended | Expected behavior, on the transfer agent’s call of an agentic warm transfer: the transfer agent decided to bridge, and the original caller was connected to the transfer target. |
transfer_cancelled | ended | On the transfer agent’s call of an agentic warm transfer: the caller was NOT connected — the transfer agent cancelled the transfer, or it timed out without a decision (e.g. the transfer target did not pick up or went to voicemail). |
call_take_over | ended | Expected behavior, a human took over the call from the agent, which permanently stops the agent for that call. |
voicemail_reached | ended | Expected behavior, if the agent is configured with voicemail settings, and voicemail is reached. |
ivr_reached | ended | Expected behavior, if the agent is configured to hang up when encountering an IVR system, and IVR is reached. |
inactivity | ended | Expected behavior, call was terminated due to the “end_call_after_silence_ms” setting reached after long inactivity. |
max_duration_reached | ended | Expected behavior, call was terminated due to maximum duration reached. |
dial_busy | not_connected | Outbound call not connected, the number dialed is busy. |
dial_failed | not_connected | Outbound call not connected, dialing failed with no or unknown sip error code. |
dial_no_answer | not_connected | Outbound call not connected, the number dialed did not answer. |
invalid_destination | not_connected | Outbound call not connected, the number dialed is invalid. Can be due to spaces or invalid characters in the number. Or it can be your telephony provider requiring a specific format (like E.164 format). |
telephony_provider_permission_denied | not_connected | Outbound call not connected, the sip trunk credentials are not authenticated. |
telephony_provider_unavailable | not_connected | Outbound call not connected, the telephony provider is unavailable. |
sip_routing_error | not_connected | Outbound call not connected, the sip routing is going over too many hops or is in a loop. |
marked_as_spam | not_connected | Outbound call not connected, the number dialed is marked as spam. See Spam Likely Overview. |
user_declined | not_connected | Outbound call not connected, user declined the call. |
concurrency_limit_reached | error | Error, concurrency limit reached, add a retry with exponential backoff. Or consider enterprise plan. |
no_concurrency_fallback | ended | Inbound call could not get a concurrency slot and was transferred to the configured fallback number. |
no_valid_payment | error | Error, no valid payment registered on file, or service shut down due to bill overdue. |
scam_detected | error | Error, scam detected for that particular agent. |
error_llm_websocket_open | error | Error, LLM websocket did not open between Retell server and your backend. Likely because the Custom LLM URL is incorrect or your LLM server is unreachable. See custom LLM troubleshooting. |
error_llm_websocket_lost_connection | error | Error, LLM websocket connection broke during the call. Often a missing ping_pong echo or a host idle timeout. See custom LLM troubleshooting. |
error_llm_websocket_runtime | error | Error, LLM websocket received a closing signal other than 1000 from your server. |
error_llm_websocket_corrupt_payload | error | Error, LLM websocket received unspecified payload, such as a binary frame instead of text. |
error_no_audio_received | error | Error, has not received audio from Twilio or web frontend for a while after connection has established. |
error_asr | error | Error, Retell’s ASR encountered a problem. |
error_retell | error | Error, unspecified Retell side problem. |
error_unknown | error | Error, unknown error. |
error_user_not_joined | error | Error, user did not join web call within 30s after calling startWebCall. |
registered_call_timeout | error | Error, phone call is 5 minutes or more apart from registration. |