curl -X POST 'https://api.elevenlabs.io/v1/convai/twilio/register-call' \
  -H "xi-api-key: $ELEVENLABS_API_KEY" \
  -H 'Content-Type: application/json' \
  -d '{
  "agent_id": "string",
  "from_number": "string",
  "to_number": "string",
  "direction": "inbound",
  "conversation_initiation_client_data": {
    "conversation_config_override": {
      "agent": {
        "first_message": "Hello, how can I help you today?",
        "language": "en",
        "prompt": {
          "knowledge_base": [],
          "llm": "gemini-2.0-flash-001",
          "prompt": "You are a helpful assistant that can answer questions about the topic of the conversation.",
          "tool_ids": []
        }
      },
      "asr": {
        "keywords": [
          "hello",
          "world"
        ]
      },
      "conversation": {
        "max_duration_seconds": 600
      },
      "tts": {
        "model_id": "eleven_turbo_v2",
        "pronunciation_dictionary_locators": [],
        "similarity_boost": 0.8,
        "speed": 1,
        "stability": 0.5,
        "voice_id": "cjVigY5qzO86Huf0OWal"
      },
      "turn": {
        "soft_timeout_config": {
          "message": "Hhmmmm...yeah."
        }
      }
    },
    "custom_llm_extra_body": {},
    "user_id": "string",
    "source_info": {
      "source": "unknown",
      "version": "string"
    },
    "branch_id": "string",
    "environment": "string",
    "starting_workflow_node_id": "string",
    "procedure_ids": [
      "string"
    ],
    "dynamic_variables": {}
  }
}'

# POST /v1/convai/twilio/register-call (ElevenLabs API)
Base URL: https://api.elevenlabs.io
Auth: xi-api-key: <ELEVENLABS_API_KEY>
Last verified: 2026-09-03

> Register A Twilio Call And Return Twiml

## Critical Gotchas
* Authentication uses the non-standard `xi-api-key` header, not `Authorization: Bearer`. Sending a Bearer token returns HTTP 401.
* Text-to-speech responses are raw binary audio, not JSON. Write the body to a file (`--output speech.mp3`) rather than parsing it.

## cURL
curl -X POST 'https://api.elevenlabs.io/v1/convai/twilio/register-call' \
  -H "xi-api-key: $ELEVENLABS_API_KEY" \
  -H 'Content-Type: application/json' \
  -d '{"agent_id":"string","from_number":"string"}'

## Parameters
| Name | In | Type | Required | Description |
| :--- | :--- | :--- | :--- | :--- |
| agent_id | body | string | Yes | Request body field agent_id. |
| from_number | body | string | Yes | Request body field from_number. |
| to_number | body | string | Yes | Request body field to_number. |
| direction | body | string | No | Request body field direction. |

## Response (200 OK)
"string"

---
Need an API key? Get one at https://elevenlabs.io/app/sign-up

POST

/v1/convai/twilio/register-call

ElevenLabs API

Base URL: https://api.elevenlabs.io
Auth: xi-api-key: <ELEVENLABS_API_KEY>
Last verified: 2026-09-03 · upstream hash matched

Actions

Agents: curl -H "Accept: text/markdown" this URL
→ 227 tokens · Vary: Accept

Critical gotchas

Authentication uses the non-standard xi-api-key header, not Authorization: Bearer. Sending a Bearer token returns HTTP 401.

Text-to-speech responses are raw binary audio, not JSON. Write the body to a file (--output speech.mp3) rather than parsing it.

cURL

curl -X POST 'https://api.elevenlabs.io/v1/convai/twilio/register-call' \  -H "xi-api-key: $ELEVENLABS_API_KEY" \  -H 'Content-Type: application/json' \  -d '{  "agent_id": "string",  "from_number": "string",  "to_number": "string",  "direction": "inbound",  "conversation_initiation_client_data": {    "conversation_config_override": {      "agent": {        "first_message": "Hello, how can I help you today?",        "language": "en",        "prompt": {          "knowledge_base": [],          "llm": "gemini-2.0-flash-001",          "prompt": "You are a helpful assistant that can answer questions about the topic of the conversation.",          "tool_ids": []        }      },      "asr": {        "keywords": [          "hello",          "world"        ]      },      "conversation": {        "max_duration_seconds": 600      },      "tts": {        "model_id": "eleven_turbo_v2",        "pronunciation_dictionary_locators": [],        "similarity_boost": 0.8,        "speed": 1,        "stability": 0.5,        "voice_id": "cjVigY5qzO86Huf0OWal"      },      "turn": {        "soft_timeout_config": {          "message": "Hhmmmm...yeah."        }      }    },    "custom_llm_extra_body": {},    "user_id": "string",    "source_info": {      "source": "unknown",      "version": "string"    },    "branch_id": "string",    "environment": "string",    "starting_workflow_node_id": "string",    "procedure_ids": [      "string"    ],    "dynamic_variables": {}  }}'

Get a free ElevenLabs API key → sponsored

Parameters

Name	In	Type	Required	Description
agent_id	body	string	Yes	Request body field agent_id.
from_number	body	string	Yes	Request body field from_number.
to_number	body	string	Yes	Request body field to_number.
direction	body	string	No	Request body field direction.
conversation_initiation_client_data	body	object	No	Request body field conversation_initiation_client_data.

Response 200 OK

"string"