21401: Invalid Phone Number

The phone number you specified was not a valid SMS-enabled phone number or alphanumeric sender ID.

If a phone number was used, this number must be one you have purchased from or ported to Twilio in E.164 format.

Alphanumeric sender IDs can only be used with accepted characters when messaging countries where this feature is supported.

The phone number is not supported in North America.

Try using a different phone number: https://www.twilio.com/phone-numbers