> ## Documentation Index > Fetch the complete documentation index at: https://docs.retellai.com/llms.txt > Use this file to discover all available pages before exploring further. # Debug call disconnection > Diagnose why a Retell call disconnected — look up the `disconnection_reason` in the dashboard or Get Call API and follow the table of causes and fixes. Open the call in [Call History](/features/session-history) or retrieve it with the [Get Call API](/api-references/get-call) to find its disconnection reason. Call detail page in the Retell Dashboard showing the disconnection reason for a call. ## Diagnosing disconnection reasons Find the reason in the table below, then follow the fix. For deeper diagnosis of specific cases: * **`not_connected` outbound calls** (`dial_failed`, `invalid_destination`, spam blocks, and other SIP failures) — see [debug outbound connection issues](/reliability/debug-outbound-call). * **SIP-level signaling and media** — inspect the call's PCAP file, covered in [debug SIP calls using PCAP files](/reliability/debug-calls-pcap). 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](/build/conversation-flow/call-transfer-node): 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](/build/conversation-flow/call-transfer-node): 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](/build/handle-voicemail), and voicemail is reached. | | `ivr_reached` | ended | Expected behavior, if the agent is configured to [hang up when encountering an IVR system](/build/handle-voicemail#ivr-hangup), 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](/deploy/concurrency#max-call-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](/build/telephony/call_efficiency_overview). | | `user_declined` | not\_connected | Outbound call not connected, user declined the call. | | `concurrency_limit_reached` | error | Error, [concurrency limit](/deploy/concurrency) 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](/integrate-llm/troubleshooting#connection-failures). | | `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](/integrate-llm/troubleshooting#the-call-drops-after-a-few-seconds). | | `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 been 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. |