---
title: "Subscribe to User Defined Messages for a given Call SID."
method: POST
path: "/2010-04-01/Accounts/{AccountSid}/Calls/{CallSid}/UserDefinedMessageSubscriptions.json"
tags: ["Api20100401UserDefinedMessageSubscription"]
---

# Subscribe to User Defined Messages for a given Call SID.

`POST /2010-04-01/Accounts/{AccountSid}/Calls/{CallSid}/UserDefinedMessageSubscriptions.json`

## Request

- Base URL: `https://api.twilio.com`
- URL: `https://api.twilio.com/2010-04-01/Accounts/{AccountSid}/Calls/{CallSid}/UserDefinedMessageSubscriptions.json`
- Auth: HTTP basic

Subscribe to User Defined Messages for a given Call SID.

## Path parameters

- `AccountSid` string, required
- `CallSid` string, required

## Request body `application/x-www-form-urlencoded`

- object
  - `Callback` string, uri, required: The URL we should call using the `method` to send user defined events to your application. URLs must contain a valid hostname (underscores are not permitted).
  - `IdempotencyKey` string: A unique string value to identify API call. This should be a unique string value per API call and can be a randomly generated.
  - `Method` 'GET' | 'POST', http-method: The HTTP method Twilio will use when requesting the above `Url`. Either `GET` or `POST`. Default is `POST`.

## Response `201`

Created

- ApiV2010AccountCallUserDefinedMessageSubscription
  - `account_sid` string, nullable: The SID of the [Account](https://www.twilio.com/docs/iam/api/account) that subscribed to the User Defined Messages.
  - `call_sid` string, nullable: The SID of the [Call](https://www.twilio.com/docs/voice/api/call-resource) the User Defined Message Subscription is associated with. This refers to the Call SID that is producing the User Defined Messages.
  - `sid` string, nullable: The SID that uniquely identifies this User Defined Message Subscription.
  - `date_created` string, date-time-rfc-2822, nullable: The date that this User Defined Message Subscription was created, given in RFC 2822 format.
  - `uri` string, nullable: The URI of the User Defined Message Subscription Resource, relative to `https://api.twilio.com`.

## Changes

- **2024-04-18** (v2010) `cf63f47f41aa`: 4 breaking
  - removed the enum value `DELETE` of the request property `Method`
  - removed the enum value `HEAD` of the request property `Method`
  - removed the enum value `PATCH` of the request property `Method`
  - removed the enum value `PUT` of the request property `Method`

[Operation history](https://skmtc.dev/twilio/apis/twilio-api/changes/2010-04-01/Accounts/:AccountSid/Calls/:CallSid/UserDefinedMessageSubscriptions.json/post.md)

---

[API](https://skmtc.dev/twilio/apis/twilio-api.md) - [All operations](https://skmtc.dev/twilio/apis/twilio-api/llms.txt) - [OpenAPI document](https://skmtc.dev/twilio/apis/twilio-api/revisions/bfdf249a1298?raw)