Youtube Content ID API总是返回Not Found

My account is connected to a CMS but I can't see Youtube Content ID in API Library. However, I see it in my Enabled APIs!! (It appeared after I try "Authorize requests using OAuth 2.0" in Youtube Content ID API reference doc). I can test the API in reference doc and it shows data from my CMS. But when I call the API from my program, the response is always like this:

{
 "error": {
  "errors": [
   {
    "domain": "global",
    "reason": "notFound",
    "message": "Not Found"
   }
  ],
  "code": 404,
  "message": "Not Found"
 }
}

This is my implementation using Go:

func TestYoutubeAPI(w http.ResponseWriter, r *http.Request)  {
    data, err := ioutil.ReadFile("./google-service-key.json")
    if err != nil {
        log.Fatal(err)
    }
    config, err := google.JWTConfigFromJSON(data, "https://www.googleapis.com/auth/youtubepartner", "https://www.googleapis.com/auth/youtube.force-ssl", "https://www.googleapis.com/auth/youtube")
    if err != nil {
        log.Fatal(err)
    }
    client := config.Client(oauth2.NoContext)

    request, _ := http.NewRequest("GET", "https://www.googleapis.com/youtube/partner/v1/assetSearch", nil)
    request.Header.Add("Accept", "application/json")

    query := request.URL.Query()
    query.Add("createdAfter","2015-01-29T23:00:00Z")
    query.Add("key", "XXX")
    request.URL.RawQuery = query.Encode()

    response, err := client.Do(request)

    if err != nil {
        fmt.Fprintln(w, err)
    } else {
        responseBody, _ := ioutil.ReadAll(response.Body)
        fmt.Println(response.Status)
        fmt.Fprintln(w, string(responseBody))
    }
}

Other APIs (Youtube Data API) work fine with this code. However, I can't get my expected result with Youtube Content ID API.

Anyone got experience in this please help me. Thank you.

I found the answer!

Because I used Google Service Account to interact with Google API. It seems to create a new user account. So that I have to grant permission on Youtube CMS by adding Service account client email to Youtube CMS. Finally, I can access Youtube CMS using the API.