409 when creating content fragment in AEMaacs

[JonnyMathias21]

Hi All, 

Please can someone put me out of my misery. I'm trying to capture the data for a content fragment on a Workfront custom form and then call AEM assets API to create a content fragment but I keep getting a 409 and I can't work out why. I'm hitting the author (https://author-XXXXX-XXXXX.adobeaemcloud.com/api/assets/demo-folder/workfront-integration-poc/CF3 with a post request but everything I try it's returning a 409 - I've put the body of the request below encase it's that.

{
   "properties":{
      "description":"This is my description",
      "title":"This is my title",
      "cq:model":"PathToModel",
      "elements":{
         "reference":{
            "value":[
               "XXXXXXX"
            ]
         },
         "title":{
            ":type":"string",
            "value":"this is my title, there are many titles like it."
         },
         "description":{
            ":type":"string",
            "value":"this is my description, there are many descriptions like it."
         },
         "tags":{
            "value":[
               "workfront-tags/demoTag"
            ]
         }
      }
   }
}