POST request to training API create workout endpoint returns an undescriptive 500 error message!

I passed the authorization process and made a call to post - https://apis.garmin.com/training-api/workout to create a work out at which point I got some errors about the structure of my body which I fixed. Then I started getting a 500 error message An internal server error occurred. Support told me its probably my JSON body object but it seems ok to me. Any help would be appriciated.  

Here is my JSON object 

{
  "workoutName": "Morning Run",
  "description": "A simple morning run workout",
  "sport": "RUNNING",
  "steps": [
  {
   "type": "WorkoutStep",
   "stepType": "Warmup",
   "durationType": "TIME",
   "durationValue": 600,
   "targetType": "SPEED",
   "targetValue": 5.5,
   "intensity": "WARMUP"
 },
 {
  "type": "WorkoutStep",
  "stepType": "Main Set",
  "durationType": "DISTANCE",
  "durationValue": 5000,
  "targetType": "HEART_RATE",
  "targetZone": 3,
  "intensity": "ACTIVE"
 },
 {
 "type": "WorkoutStep",
 "stepType": "Cooldown",
 "durationType": "TIME",
 "durationValue": 300,
 "intensity": "COOLDOWN"
 }
]}