curl --request POST \
  --url https://studio-api.onlytraffic.com/api/external/v1/accounts/{username}/content \
  --header 'Content-Type: multipart/form-data' \
  --header 'X-API-Key: <api-key>' \
  --form 'files=<string>' \
  --form files.items='@example-file'

{
  "success": true,
  "data": {
    "uploaded": [
      {
        "id": 123,
        "thumbnail_url": "<string>"
      }
    ],
    "failed": [
      {
        "file": "<string>",
        "error": "<string>"
      }
    ]
  }
}