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# Custom Channel

## Overview

Custom Channel connects an external messaging system to an ElevenLabs agent. Send user messages to an ElevenLabs webhook, then receive agent replies on your own HTTPS endpoint.

> **Warning**
>
> Custom Channel is in alpha.

> **Warning**
>
> Custom Channel is unavailable for agents or workspaces using zero-retention mode.

## Capabilities

| Capability                | Support                                                       |
| ------------------------- | ------------------------------------------------------------- |
| Zero retention mode (ZRM) | Not supported — unavailable for ZRM workspaces and ZRM agents |
| Attachments in messages   | Not supported — messages are text only                        |

## Setup

#### Open Custom Channel

Open your agent, select **Channels**, choose **Custom Channel**, and click **Add trigger**.

#### Configure the trigger

Select an existing connection or create one, then enter the **Reply Webhook URL**.

#### Copy the credentials

Click **Add**, then copy the **Inbound Webhook URL**, **Inbound Secret**, and **Outbound Signing Secret**.

#### Configure your service

Send user messages to the inbound webhook URL with the inbound secret in `X-Webhook-Secret`. Use the outbound signing secret to verify each reply.

## Send a message

Send a `POST` request to the generated webhook URL:

```text
POST /v1/convai/api-integrations/custom_channel/triggers/{trigger_connection_id}/async_message
X-Webhook-Secret: <inbound-secret>
Content-Type: application/json
```

```json
{
  "data": {
    "type": "user_message",
    "text": "Where is my order?",
    "user_identifier": "customer_8427"
  },
  "user_message_id": "msg_01k1e6z3f4t8n9c2",
  "dynamic_variables": {
    "order_id": "order_72491"
  }
}
```

| Field                  | Required | Description                                                                              |
| ---------------------- | -------- | ---------------------------------------------------------------------------------------- |
| `data.type`            | Yes      | Must be `user_message`.                                                                  |
| `data.text`            | Yes      | Non-empty user message.                                                                  |
| `data.user_identifier` | No       | Identifier for the external user.                                                        |
| `user_message_id`      | Yes      | Non-empty idempotency key supplied by your system.                                       |
| `conversation_id`      | No       | Include the returned ID to continue a conversation. Omit it to start a new conversation. |
| `dynamic_variables`    | No       | Dynamic variables supplied to the agent for this turn.                                   |

ElevenLabs returns `202 Accepted` before processing the turn:

```json
{
  "conversation_id": "conv_01k1e72d4x8p6v3m",
  "status": "queued"
}
```

To continue the conversation, send another request with that `conversation_id` and a new `user_message_id`.

## Receive replies

ElevenLabs sends a `POST` request to the reply webhook URL after each turn:

```json
{
  "version": "1",
  "conversation_id": "conv_01k1e72d4x8p6v3m",
  "user_message_ids": ["msg_01k1e6z3f4t8n9c2"],
  "status": "completed",
  "data": [
    {
      "type": "agent_response",
      "event": {
        "agent_response": "Your order is scheduled to arrive tomorrow.",
        "response_id": "9f2c1a7e-4b3d-4e8a-9c1f-2d6b8e0a5f31",
        "event_id": 4
      }
    },
    {
      "type": "agent_tool_response",
      "event": {
        "tool_name": "end_call",
        "tool_call_id": "toolu_01k1e70r4b8y",
        "tool_type": "system",
        "event_id": 4,
        "is_called": true,
        "is_error": false,
        "is_blocked": false,
        "status": "success"
      }
    }
  ],
  "error": null
}
```

If processing fails, `status` is `failed`, `data` is `[]`, and `error` contains a description.

`data` lists events in turn order. Every item has a `type` and an `event`:

* `agent_response` contains one agent utterance. `response_id` uniquely identifies the utterance, while `event_id` associates it with a turn. Join the `agent_response` values if your channel renders one text bubble per turn.
* `agent_tool_response` reports a tool outcome and shares the turn's `event_id`. Its `status` is `success`, `error`, `blocked`, or `skipped`. A response with `tool_type: "system"`, `tool_name: "end_call"`, and `status: "success"` means the agent ended the conversation.

Multiple inbound messages can be coalesced into one turn. `user_message_ids` lists the user message IDs this reply is answering.

## Verify reply signatures

Each reply includes an `ElevenLabs-Signature` header:

```text
t=1753876800,v0=<hex-digest>
```

The digest is an HMAC-SHA256 signature over `{timestamp}.{raw_request_body}` using the outbound signing secret. Verify the raw body before parsing JSON and reject stale timestamps.

```python
import hashlib
import hmac
import time


def verify_signature(raw_body: bytes, header: str, secret: str) -> None:
    values = dict(part.split("=", 1) for part in header.split(","))
    timestamp = values["t"]
    if abs(time.time() - int(timestamp)) > 30 * 60:
        raise ValueError("Stale webhook signature")

    expected = hmac.new(
        secret.encode(),
        timestamp.encode() + b"." + raw_body,
        hashlib.sha256,
    ).hexdigest()
    if not hmac.compare_digest(expected, values["v0"]):
        raise ValueError("Invalid webhook signature")
```

```typescript
import { createHmac, timingSafeEqual } from "node:crypto";

export function verifySignature(rawBody: Buffer, header: string, secret: string): void {
  const values = Object.fromEntries(header.split(",").map((part) => part.split("=", 2)));
  const timestamp = values.t;
  if (!timestamp || Math.abs(Date.now() / 1000 - Number(timestamp)) > 30 * 60) {
    throw new Error("Stale webhook signature");
  }

  const expected = createHmac("sha256", secret).update(`${timestamp}.`).update(rawBody).digest();
  const received = Buffer.from(values.v0 ?? "", "hex");
  if (received.length !== expected.length || !timingSafeEqual(expected, received)) {
    throw new Error("Invalid webhook signature");
  }
}
```

## Delivery behavior

ElevenLabs makes three in-process delivery attempts at approximately 0, 0.5, and 2 seconds. A `2xx` response marks delivery successful.

Request bodies are limited to 256 KiB.