curl -L -X POST 'https://flux.postacksolutions.com/api/files/upload' \
  -H 'Authorization: Bearer YOUR_ACCESS_TOKEN' \
  -F 'file=@/path/to/file.jpg'

{
  "fileId": "file_123",
  "url": "https://flux.postacksolutions.com/api/files/file_123",
  "filename": "image.jpg",
  "mimeType": "image/jpeg",
  "size": 12345
}