The ID of the scheduled text message, as returned by the sendSMS method.
an array with 2 keys: 'scheduled_id', 'status' e.g. $result['scheduled_id']
String: The unique ID of the scheduled message.
The status of the message, i.e., DELETED.
Specific error codes:
The provided Resource ID is not valid or is malformed.
This can have multiple meanings: either 1) the scheduled message id doesn't exist or belongs to other account than the one using the REST API; or 2) the scheduled message has already been sent and, as so, can't be deleted.