---
page_type: error
code: 21604
message: "21604: The destination 'To' phone number is required to send an SMS"
level: ERROR
---

## Description

## Error - 21604

### '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`.