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