---
"@context": https://schema.org
"@type": TechArticle
"@id": https://www.twilio.com/docs/api/errors/21604#article
headline: "21604: The destination 'To' phone number is required to send an SMS"
url: https://www.twilio.com/docs/api/errors/21604
inLanguage: en
dateModified: 2026-03-11T18:38:39.000Z
author:
  "@type": Organization
  name: Twilio Developer Education Team
publisher:
  "@type": Organization
  name: Twilio
---

# 21604: The destination 'To' phone number is required to send an SMS

Log Type: APPLICATION

Log Level: ERROR

## Description

### 'To' phone number is required to send a Message

Make sure to specify a valid phone number as the recipient of the message.

### Possible causes

* 'To' phone number is not specified
* Your request is not formatted as `application/x-www-form-urlencoded`

### Possible solutions

* Make sure to include a 'To' phone number
* Check that you are submitting your request as `application/x-www-form-urlencoded` and not as `json`.