We have also a documentation section available for how the API works: Reference 1

The Inference Toolkit accepts inputs in the inputs key, and supports additional  pipelines  parameters in the parameters key. You can provide any of the supported kwargs from pipelines as parameters .

{
  "inputs": "This sound track was beautiful! It paints the senery in your mind so well I would recomend it
  even to people who hate vid. game music!", 
 "parameters": {
        "return_all_scores": True
  }
}