---
page_type: error
code: 21614
message: "21614: 'To' number is not a valid mobile number"
level: ERROR
product: Programmable SMS
---

## Description

You have attempted to send a SMS with a 'To' number that is not a valid mobile number. It is likely that the number that you have specified is a landline number or is an invalid number.

### Possible Causes

- The number you provided may be a landline number.
- The number you provided may be invalid or formatted incorrectly.
- If you are attempting to send SMS to Internet of Things (IoT) or machine-to-machine (M2M) numbers, the numbers may use a non-standard format that Twilio has not added to our number validation system yet.

### Possible Solutions

- Confirm that the number you are sending to is not a landline, using the [Lookup API](/docs/lookup/v2-api).
- Please verify you have provided a valid mobile number in proper [E.164 format](https://support.twilio.com/hc/en-us/articles/223183008-Formatting-International-Phone-Numbers).
- If you are attempting to send SMS to an IoT or M2M number, check whether the number format is different from the standard mobile numbers in that country or locality. Often, these numbers have additional digits or unusual formats which do not pass Twilio's number validation. If you believe this is the issue, please [contact Twilio Support](https://www.twilio.com/help/contact) for assistance.