---
"@context": https://schema.org
"@type": TechArticle
"@id": https://www.twilio.com/docs/api/errors/21709#article
headline: "21709: Alpha Sender ID is Invalid or Not Authorized for this Messaging Service"
url: https://www.twilio.com/docs/api/errors/21709
inLanguage: en
dateModified: 2026-03-11T18:38:39.000Z
author:
  "@type": Organization
  name: Twilio Developer Education Team
publisher:
  "@type": Organization
  name: Twilio
---

# 21709: Alpha Sender ID is Invalid or Not Authorized for this Messaging Service

Log Type: APPLICATION

Log Level: ERROR

## Description

The Alpha Sender ID being added to a Messaging Service is invalid or Alpha Sender IDs have not been enabled for this Messaging Service.

### Possible causes

* The Messaging Service is not enabled to support Alpha Sender IDs.
* The Alpha Sender ID being added to a Messaging Service is invalid. Alphanumeric Sender IDs may be up to 11 characters. They may not be only numbers. Refer to [this page](https://support.twilio.com/hc/en-us/articles/223133867-Using-Alphanumeric-Sender-ID-with-Messaging-Services) for acceptable characters.

### Possible solutions

* Follow [these steps](https://support.twilio.com/hc/en-us/articles/223181348-Alphanumeric-Sender-ID-for-Twilio-Programmable-SMS#h_01F4SK0WYHA75NK1DNXGTCFMP8) to verify your Messaging Service is enabled to support Alpha Sender IDs. If it is not, please reach out to Support.
* Verify the Alpha Sender ID you are trying to add to the Messaging Service is valid. View formatting requirements [here](https://support.twilio.com/hc/en-us/articles/223181348-Alphanumeric-Sender-ID-for-Twilio-Programmable-SMS#h_01F4SK0R6NH8AQW36Y4BR16FVA).