Sending Concurrent Requests to SAP endpoint is Timed out from Strapi endpoint

Question

I have Function in C# Which posts a certain ledger in a JSON format to a SAP endpoint. I have 12 such JSON that needs to be posted. But as it happens 11/12 JSON post successfully, but the last one gets timed out. From my side I have increased the Max timeout limit to 5 minutes The timed-out response says

A connection attempt failed because the connected party did not properly respond after a period of time or established connection failed because connected host has failed to respond. (interfaces.confidential.com:443).

Also the timeout response returns 200 status code even after timing out.

I also have a retry policy in place if the response is not 200.

public async Task<string> InvokePostAsync(string jsonString,string clientId, string fileName)
 {
     string result = null;
     HttpResponseMessage response = new HttpResponseMessage();
     string submissionTime = null;
     string responseTime = null;

     try
     {
         if (jsonString.IsNotNullEmptyOrWhitespace()) {
             var client = new HttpClient();
             client.Timeout = TimeSpan.FromMinutes(5); // max timeout limit set to 5 minutes

             var retryPolicy = Policy
                 .HandleResult<HttpResponseMessage>(r => r.StatusCode == System.Net.HttpStatusCode.InternalServerError)
                 .WaitAndRetryAsync(3, retryAttempt => TimeSpan.FromSeconds(3));
             submissionTime = DateTime.Now.ToString(); //retry after 3 sec if not 200 status 
             response = await retryPolicy.ExecuteAsync(async () =>
             {
                 var request = new HttpRequestMessage(HttpMethod.Post, new Uri( _appSettings.postEndpoint) );
                 request.Headers.Add("Accept", "application/json");
                 request.Headers.Add("Authorization", $"Basic {_appSettings.AuthToken}");
                 request.Content = new StringContent(jsonString);

                 return await client.SendAsync(request);
             });
             responseTime = DateTime.Now.ToString();
             response.EnsureSuccessStatusCode();
             result = await response.Content.ReadAsStringAsync();

             _logger.LogInformation($"Post result for client {clientId}:" + result);
         }
         
         return await createEmailMessageforClient(true,clientId,submissionTime,responseTime,fileName,result,(int)response.StatusCode);
     }
     catch (Exception ex)
     {
         responseTime = DateTime.Now.ToString(); 
         _logger.LogError($"Error while posting web service for client: {clientId} Exception: {ex.Message}");
         return await createEmailMessageforClient(false, clientId, submissionTime, responseTime, fileName, ex.Message, (int)response.StatusCode);
     }
 }

I feel like from my side I have done Everything fine, And I think The SAP endpoint has a rate limit set to it. Please let me know if I can tackle this issue from my code itself. OR is it only configurable using the SAP interface?