问.net 使用滑动验证码为什么一直报签名错误？

try
            {
                var cred = new Credential
                {
                    SecretId = "xxx",
                    SecretKey = "xxx"
                };

                var httpProfile = new HttpProfile
                {
                    Endpoint = "captcha.tencentcloudapi.com"
                };

                var clientProfile = new ClientProfile
                {
                    HttpProfile = httpProfile
                };

                string strParams = "{\"CaptchaType\":9,\"Ticket\":\"t02q8BvXw57fktKYywZnx4p_RyGiIhOYAhKMWQGAKUOiF7ULk3ZolMM-Xksm0xWQo1VIG4xhs5V9qEwSpOyuQQv_7brDbEfvIBjWhm4MPVFsSiHgYzRDNscmA**\",\"UserIp\":\"127.0.0.1\",\"Randstr\":\"@aNa\",\"CaptchaAppId\":xx,\"AppSecretKey\":\"xx**\"}";
                var client = new CaptchaClient(cred, "ap-shanghai", clientProfile);
                var req = AbstractModel.FromJsonString<DescribeCaptchaResultRequest>(strParams);
                var resp = client.DescribeCaptchaResult(req).ConfigureAwait(false).GetAwaiter().GetResult();

                var res = AbstractModel.ToJsonString(resp);
                Console.WriteLine(res);
            }
            catch (TencentCloudSDKException ex)
            {
                Console.WriteLine(ex.ToString());
            }