---
title: "Call Conversation Start Failed"
method: POST
path: "callConversationStartFailed"
tags: ["Callbacks"]
---

# Call Conversation Start Failed

`POST callConversationStartFailed` (webhook)

Emitted when an AI assistant requested with an `answer` or `dial` command (`assistant.id`) could not be started after the call was answered, for example because the assistant ID does not exist. No conversation is created, so neither `call.conversation.created` nor `call.conversation.ended` is sent for this attempt. The call stays answered: use this event to continue the call, for example by transferring it, playing a message, or hanging up. `data.payload.reason` is `invalid_request` when the request was rejected and `service_error` otherwise.

This webhook uses Telnyx headers (telnyx-timestamp, telnyx-signature-ed25519) that are compatible with Standard Webhooks specification for SDK generation. Custom validation logic can map these to standard webhook-timestamp and webhook-signature equivalents. See https://github.com/standard-webhooks/standard-webhooks for details.

## Headers

- `telnyx-timestamp` integer, required: Unix timestamp for replay attack prevention
- `telnyx-signature-ed25519` string, required: Ed25519 signature of timestamp|payload for verification

## Payload

- CallConversationStartFailedEvent
  - `data` CallConversationStartFailed: The AI assistant requested for the call could not be started, so no conversation was created. No `call.conversation.created` or `call.conversation.ended` is sent for this attempt.
    - `record_type` 'event': Identifies the type of the resource.
    - `event_type` 'call.conversation.start_failed': The type of event being delivered.
    - `id` string, uuid: Unique identifier for the event.
    - `occurred_at` string, date-time: ISO 8601 datetime of when the event occurred.
    - `created_at` string, date-time: Timestamp when the event was created in the system.
    - `payload` object
      - `call_control_id` string: Call ID used to issue commands via Call Control API.
      - `call_leg_id` string: ID that is unique to the call leg.
      - `call_session_id` string: ID that is unique to the call session (group of related call legs).
      - `connection_id` string: Call Control App ID (formerly Telnyx connection ID) used in the call.
      - `client_state` string: Base64-encoded state received from a command.
      - `from` string: The caller's number or identifier.
      - `to` string: The callee's number or SIP address.
      - `calling_party_type` 'pstn' | 'sip': The type of calling party connection.
      - `assistant_id` string: Identifier of the AI assistant that failed to start.
      - `reason` 'invalid_request' | 'service_error': Why the conversation could not be started. `invalid_request`: the assistant request was rejected, for example because the assistant ID does not exist. `service_error`: the assistant could not be started because of an error on the Telnyx side.

## Acknowledgement `200`

The server must return an HTTP 200, otherwise we will reattempt delivery at the failover webhook URL.

---

[API](https://skmtc.dev/team-telnyx/apis/telnyx-api-2.md) - [All operations](https://skmtc.dev/team-telnyx/apis/telnyx-api-2/llms.txt) - [OpenAPI document](https://skmtc.dev/team-telnyx/apis/telnyx-api-2/revisions/f82938f53ff4?raw)