Callbacks

Call Conversation Start Failed

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.

postWebhookcallConversationStartFailed

Headers

telnyx-timestampinteger required

Unix timestamp for replay attack prevention

Unix timestamp (seconds since epoch) of when the webhook was sent - compatible with webhook-timestamp

telnyx-signature-ed25519string required

Ed25519 signature of timestamp|payload for verification

Base64 encoded Ed25519 signature for webhook verification - compatible with webhook-signature

Payload

Example payload

{
  "data": {
    "record_type": "event",
    "event_type": "call.conversation.start_failed",
    "id": "3f1c2a9e-8d4b-4c6e-9a7f-1b2c3d4e5f60",
    "occurred_at": "2025-05-29T13:35:38.817785Z",
    "created_at": "2025-05-29T13:35:38.927621Z",
    "payload": {
      "assistant_id": "assistant-d9082b56-ba2d-4ad1-a50c-58661eb1463d",
      "call_control_id": "v3:HDR1vQHx697hpP9xZ0bhlbUOWPFPDtPcxw-nuSMuC6mGVpb0euoklQ",
      "call_leg_id": "cc29cce6-3c91-11f0-a8e5-02420aef3d20",
      "call_session_id": "cc29c8d6-3c91-11f0-aa7c-02420aef3d20",
      "client_state": "g3QAAAACbQAAAAtkYXRhX2NlbnRlcm0AAAADY2gxbQAAAApkZXBsb3ltZW50bQAAAARiYXNl",
      "connection_id": "2694492062593582591",
      "from": "+13124287921",
      "to": "+13125550100",
      "reason": "invalid_request"
    }
  }
}

Response

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

Changes

Webhooks have no change history: a webhook is keyed by its event name rather than a path and method, so no recorded change can name it.