如何修复C＃中的“需要验证码验证”错误

Question

在确认我不是机器人复选框后，将显示Java脚本警报“ localhost：12345说空”，然后在警报上单击“确定”，然后单击“提交”按钮，仍然说“ Captcha即使经过验证，也需要验证。

这是我的“与我们联系”页面，即使我得到了最初以为是问题的新钥匙，验证仍然无法进行。 C＃

public partial class _default : System.Web.UI.Page
    {
        classes.Common xCommon = new classes.Common();
        classes.Email xEmail = new classes.Email();

        protected static string ReCaptcha_Key = "6LczL3QUAAAAAGnY8hnA-hgRjHV0q---------";
        protected static string ReCaptcha_Secret = "6LczL3QUAAAAADWlVe0IKVERdq----------";

        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void btn_Contact_Submit_Click(object sender, EventArgs e)
        {
            xEmail.ContactUs_Email(txt_Contact_Name.Text, txt_Contact_Email.Text, txt_Contact_No.Text, ddl_Branch.SelectedItem.ToString(), ddl_Division.SelectedValue,ddl_Type.SelectedValue,txt_Contact_Message.Text, ddl_Branch.SelectedValue);

            ltr_MessageReturn.Text = xCommon.Return_Message("contactus", "");
            btn_Contact_Submit.Visible = false;
        }

        [WebMethod]
        public static string VerifyCaptcha(string response)
        {
            string url = "https://www.google.com/recaptcha/api/siteverify?secret=" + ReCaptcha_Secret + "&response=" + response;
            return (new WebClient()).DownloadString(url);
        }
    }
}

JavaScript

 var onloadCallback = function () {
    grecaptcha.render('dvCaptcha', {
        'sitekey': '<%=ReCaptcha_Key %>',
        'callback': function (response) {
            $.ajax({
                type: "POST",
                url: "default.aspx/VerifyCaptcha",
                data: "{response: '" + response + "'}",
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                success: function (r) {
                    var captchaResponse = jQuery.parseJSON(r.d);
                    if (captchaResponse.success) {
                        $("[id*=txtCaptcha]").val(captchaResponse.success);
                        $("[id*=rfvCaptcha]").hide();
                    } else {
                        $("[id*=txtCaptcha]").val("");
                        $("[id*=rfvCaptcha]").show();
                        var error = captchaResponse["error-codes"][0];
                        $("[id*=rfvCaptcha]").html("RECaptcha error. " + error);
                    }
                }
            });
        }
    });
};
 </script>

我希望用户选择所有必需的图像以通过验证然后提交后，验证才能通过。但输出仍然显示需要验证。