You need to supply the workout description in Intervals.icu format (as you would enter it in the workout builder) or a workout file (fit, zwo etc.). You can’t supply a workout_doc.
{
"category": "WORKOUT",
"start_date_local": "2024-03-30T00:00:00",
"description": "- 2h Z2 Pace\n- 10m Z1 Pace"
}
{
"category": "WORKOUT",
"start_date_local": "2024-03-30T00:00:00",
"filename": "Woddle_Toddle.fit",
"file_contents_base64": "DiCNCG8AAAAuRklUKz9AAAEAAAMBAoQAAQAIDgcAAP8FSW50ZXJ2YWxzLmljdQBAAAEAGgMEAQAIDgcGAoQAAVdvZGRsZSBUb2RkbGUAAAFAAAEAGwcBAQACBIYDAQAFBIYGBIYHAQD+AoQAAAA27oABAAAA+AAAAQAEAAAe/A=="
}
Intervals.icu will calculate moving_time and other fields.