downloadCaptionTrack true a boolean not a caption data

[nvvinhit2020]

Hi, I would to use downloadCaptionTrack to download caption a video. However, it's just returned a Boolean value. How can I get the caption data? Thanks for your help. fetcher.performRequest(serviceName: apiNameInURL, apiVersion: apiVersionString, endpoint: "captions/(id)", queryParams: queryParams) { (JSON, error) -> () in if error != nil { completionHandler(success: false, error: error) } else { completionHandler(success: true, error: nil) } }