Api Gateway invokation

Hello AWS Support,

I am currently implementing a virtual waiting room using the "Getting Started" template and am encountering an issue when attempting to invoke the increment_serving_counter API endpoint from my .NET application. The API invocation consistently fails

Here is the relevant code snippet for the API call:

public static async Task<bool> IncrementServingCounterAsync()
        {
            string awsKeyId = "";
            string awsKeySecret = "";
            string region = "";
            string service = "execute-api";

            var endpoint = "endPoint/increment_serving_counter";

            var requestBody = new
            {
                event_id = "myEventId",
                increment_by = 1
            };

            var requestMessage = new HttpRequestMessage(HttpMethod.Post, endpoint)
            {
                Content = new StringContent(
                    Newtonsoft.Json.JsonConvert.SerializeObject(requestBody),
                    Encoding.UTF8,
                    "application/json"
                )
            };

            // Sign the request
            SignRequest(requestMessage, awsKeyId, awsKeySecret, region, service);

            using (var httpClient = new HttpClient())
            {
                var response = await httpClient.SendAsync(requestMessage);
                return response.IsSuccessStatusCode;
            }
        }

        private static void SignRequest(HttpRequestMessage request, string accessKey, string secretKey, string region, string service)
        {
            // Implement AWS Signature Version 4 signing here
            var algorithm = "AWS4-HMAC-SHA256";
            var amzDate = DateTime.UtcNow.ToString("yyyyMMddTHHmmss") + "Z";
            var dateStamp = DateTime.UtcNow.ToString("yyyyMMdd");

            // Construct canonical request
            var canonicalUri = request.RequestUri.AbsolutePath;
            var canonicalQueryString = string.Empty;
            var canonicalHeaders = $"host:{request.RequestUri.Host}\n";
            var signedHeaders = "host";
            var payloadHash = ComputeSha256Hash(request.Content.ReadAsStringAsync().Result);
            var canonicalRequest = $"{request.Method}\n{canonicalUri}\n{canonicalQueryString}\n{canonicalHeaders}\n{signedHeaders}\n{payloadHash}";

            // Create the string to sign
            var credentialScope = $"{dateStamp}/{region}/{service}/aws4_request";
            var stringToSign = $"{algorithm}\n{amzDate}\n{credentialScope}\n{ComputeSha256Hash(canonicalRequest)}";

            // Calculate the signature
            var signingKey = GetSignatureKey(secretKey, dateStamp, region, service);
            var signature = ComputeHmacSha256(signingKey, stringToSign);

            // Add authorization header to the request
            var authorizationHeader = $"{algorithm} Credential={accessKey}/{credentialScope}, SignedHeaders={signedHeaders}, Signature={signature}";
            request.Headers.Authorization = new AuthenticationHeaderValue("AWS4-HMAC-SHA256", authorizationHeader);
            request.Headers.Add("x-amz-date", amzDate);
        }

        private static string ComputeSha256Hash(string data)
        {
            using (var sha256 = SHA256.Create())
            {
                var hash = sha256.ComputeHash(Encoding.UTF8.GetBytes(data));
                return BitConverter.ToString(hash).Replace("-", "").ToLowerInvariant();
            }
        }

        private static byte[] ComputeHmacSha256(byte[] key, string data)
        {
            using (var hmac = new HMACSHA256(key))
            {
                return hmac.ComputeHash(Encoding.UTF8.GetBytes(data));
            }
        }

        private static byte[] GetSignatureKey(string key, string dateStamp, string region, string service)
        {
            var kDate = ComputeHmacSha256(Encoding.UTF8.GetBytes("AWS4" + key), dateStamp);
            var kRegion = ComputeHmacSha256(kDate, region);
            var kService = ComputeHmacSha256(kRegion, service);
            var kSigning = ComputeHmacSha256(kService, "aws4_request");
            return kSigning;
        }

I have verified that the endpoint URL and AWS credentials are correct.

Thank you for your assistance.

Best regards,

Nick Pnevmatikos