我在做沙滩app，

在app中新建收藏会有400错误返回

@POST("/ct/ucenter/collection")
Observable<BaseResponseBean> postNewCollection(@Body NewCollection data, @Header("sob_token")String token);

public class NewCollection {
                         private String name;
                         private String description;
                         private MultipartBody.Part cover;
                          private String permission;
                }

  MultipartBody.Part   通过以下得到
  private MultipartBody.Part createPartByPathAndKet(String path, String key) {
      File file = new File(path);
      RequestBody body = RequestBody.create(MediaType.parse("image/png"), file);
      MultipartBody.Part part = MultipartBody.Part.createFormData(key, file.getName(), body);
      return part;
  }

如果用postman来请求又会有415错误，说类型不对，我调整了好几个都不对

我应该怎样才能成功新建收藏夹