That start time has been filled

making a RestClient API call

No matter what time or day i enter into the start_time for one member of my teams event_type and then scehdule a meeting with me.  i get

 

{

    "title": "Invalid Argument",

    "message": "The supplied parameters are invalid.",

    "details": [

        {

            "parameter": "event.start_time",

            "message": "That start time has been filled",

            "code": "already_filled"

        }

    ]