21604: The destination 'To' phone number is required to send an SMS

Make sure to specify a valid phone number as the recipient of the message.

• 'To' phone number is not specified
• Your request is not formatted as application/x-www-form-urlencoded

• Make sure to include a 'To' phone number
• Check that you are submitting your request as application/x-www-form-urlencoded and not as json.