21607: The 'from' phone number must be the sandbox phone number for trial accounts.

While your account is in Trial mode, you can only send SMS messages from your free trial number, or the Twilio Sandbox Number.

You attempted to send an SMS from a phone number other than your trial number or the Twilio Sandbox Number.

• Send SMS from your assigned trial number or the Twilio Sandbox Number.
• Upgrade your account to remove this restriction.