---
"@context": https://schema.org
"@type": TechArticle
"@id": https://www.twilio.com/docs/api/errors/40159#article
headline: "40159: Conference Instruction does not have a valid 'status_callback_url' parameter"
url: https://www.twilio.com/docs/api/errors/40159
inLanguage: en
dateModified: 2026-06-08T11:29:20.000Z
author:
  "@type": Organization
  name: Twilio Developer Education Team
publisher:
  "@type": Organization
  name: Twilio
---

# 40159: Conference Instruction does not have a valid 'status\_callback\_url' parameter

Log Type: APPLICATION

Log Level: ERROR

## Description

This error occurs when you send a TaskRouter `conference` instruction with a `status_callback_url` value that Twilio cannot validate. Conference instructions accept Conference Participants API parameters for the worker leg, and `status_callback_url` must be a valid HTTP or HTTPS URL string.

### Possible causes

* You set `status_callback_url` to an empty string.
* You passed `status_callback_url` with the wrong data type instead of a string.
* You provided a malformed URL in `status_callback_url`.
* The URL is missing the `http://` or `https://` scheme.
* Your application generated the assignment instruction dynamically and serialized `status_callback_url` incorrectly.

### Possible solutions

* Set `status_callback_url` to a complete, well-formed HTTP or HTTPS URL string.
* Include the full scheme and host in the callback URL, for example `https://example.com/conference-events`.
* If you build assignment instructions in code, make sure `status_callback_url` is serialized as a string value.
* If you do not need conference status callbacks, omit `status_callback_url` instead of sending an empty value.
* Review the Conference Participants API parameters you pass through the TaskRouter `conference` instruction and correct any invalid callback configuration before retrying the reservation update.

#### Additional resources

* [Task Reservation Resource](/docs/taskrouter/api/reservations)
* [Conferences Participants subresource](/docs/voice/api/conference-participant-resource)
* [Assigning Tasks to Workers: Handling Assignment Callbacks](/docs/taskrouter/handle-assignment-callbacks)