---
title: "SIP Refer a call"
method: POST
path: "/calls/{call_control_id}/actions/refer"
tags: ["Call Commands"]
---

# SIP Refer a call

`POST /calls/{call_control_id}/actions/refer`

Initiate a SIP Refer on a Call Control call. You can initiate a SIP Refer at any point in the duration of a call.

**Expected Webhooks:**

- `call.refer.started`
- `call.refer.completed`
- `call.refer.failed`

## Path parameters

- `call_control_id` string, required

## Request body

- ReferRequest
  - `sip_address` string, required — The SIP URI to which the call will be referred to.
  - `client_state` string — Use this field to add state to every subsequent webhook. It must be a valid Base-64 encoded string.
  - `command_id` string — Use this field to avoid execution of duplicate commands. Telnyx will ignore subsequent commands with the same `command_id` as one that has already been executed.
  - `custom_headers` CustomSipHeader[] — Custom headers to be added to the SIP INVITE.
    - `name` string, required — The name of the header to add.
    - `value` string, required — The value of the header.
  - `sip_auth_username` string — SIP Authentication username used for SIP challenges.
  - `sip_auth_password` string — SIP Authentication password used for SIP challenges.
  - `sip_headers` SipHeader[] — SIP headers to be added to the request. Currently only User-to-User header is supported.
    - `name` 'User-to-User', required — The name of the header to add.
    - `value` string, required — The value of the header.

## Response `200`

Successful response upon making a call control command.

- object
  - `data` CallControlCommandResult
    - `result` string

## Other responses

- `422` — Unprocessable entity. The request was well-formed but could not be processed due to semantic errors. This includes validation errors, invalid parameter values, call state errors, conference errors, queue errors, recording/transcription errors, and business logic violations.
- `default` — Unexpected error

## Changes

> 81 revisions in range; 1 not diffed.

- **2026-08-17** `1571b0380bd7` — 3 breaking
  - the response's body type changed from `object` to no type for status `default`
  - the `errors/items/` response's property type changed from `object` to no type for status `default`
  - the `errors/items/code` response's property type changed from `integer` to `string`, and format from `int32` to `integer` for status `default`
- **2026-08-04** `8f5f4e537994` — 4 breaking
  - the response's body type changed from no type to `object` for status `default`
  - the `errors/items/` response's property type changed from no type to `object` for status `default`
  - the `errors/items/code` response's property type changed from `string` to `integer`, and format from `integer` to `int32` for status `default`
  - the `errors/items/source/pointer` response's property format changed from `json-pointer` to no format for status `default`

[Change history](https://skmtc.dev/team-telnyx/apis/telnyx-api-2/changes/calls/:call_control_id/actions/refer/post.md)

---

[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/f6e9ed754d05?raw)