---
page_type: error
code: 21709
message: "21709: Alpha Sender ID is Invalid or Not Authorized for this Messaging Service"
level: ERROR
product: Programmable SMS
---

## 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).