Youtube API：Go客户端：无法更改播放列表项的位置

Here is a function I have written to change the position of a playlist item:

var service *youtube.Service

func setPlaylistItemPosition(item *youtube.PlaylistItem, i int64) error {
    if item.Snippet == nil {
        return errors.New("playlist item snippet is null")
    }

    item.Snippet.Position = i
    response, err := service.PlaylistItems.Update("snippet", item).Do()
    if err != nil {
        return err
    }

    if response.Snippet.Position != i {
        return errors.New("failed to set playlist items position")
    }

    return nil
}

However, when I call this function, I get the following error:

googleapi: Error 400: {0}, unexpectedPart

Even though the documentation says "snippet" is a valid part.

Any help appreciated. Cheers.

Based on the Official Google Docs, 400 unexpectedPart the request could not be understood by the server due to request's part parameter specifies an unexpected value or due to invalid value. Do check your value parameter being request to the server.