UnityWebRequest return Unknow Error code 0

Unity Engine
1

I write a very simple script to read the string from my website:

    void Start()
    {
        StartCoroutine(SendRequest());
    }

    IEnumerator SendRequest()
    {
        UnityWebRequest uwr = UnityWebRequest.Get("https://www.gzztech.cn/");
        yield return uwr.SendWebRequest();
        if (uwr.isHttpError || uwr.isNetworkError)
        {
            Debug.Log(uwr.error + " " + uwr.responseCode);
        }
        else
        {
            Debug.Log("Get:Success");
            string a = uwr.downloadHandler.text;
            Debug.Log(a);
        }
    }

return error : “Unknown Error 0”. the url just return a very simple string. I can open the page in any brower.
what’s the wrong?Thank you!

Unity version : 2018.3.13f1

2

Verify you can connect to a site with http instead of https first.