I am trying to send a request to an ASMX service using my code. The code works perfectly on my local machine, and I receive a correct response there. Additionally, sending the request via SoapUI on the server also works as expected. However, when I execute the same code on the server, I encounter the following error:

Could not establish trust relationship for the SSL/TLS secure channel with authority 'pec.shaparak.ir'

SOAP Request in SoapUI:

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:sal="https://pec.Shaparak.ir/NewIPGServices/Sale/SaleService">
   <soapenv:Header/>
   <soapenv:Body>
      <sal:SalePaymentRequest>
         <!--Optional:-->
         <sal:requestData>
            <!--Optional:-->
            <sal:LoginAccount>**********</sal:LoginAccount>
            <sal:Amount>1046673000</sal:Amount>
            <sal:OrderId>111111111</sal:OrderId>
            <!--Optional:-->
            <sal:CallBackUrl>********</sal:CallBackUrl>
            <!--Optional:-->
            <sal:AdditionalData>?</sal:AdditionalData>
            <!--Optional:-->
            <sal:Originator>*******</sal:Originator>
         </sal:requestData>
      </sal:SalePaymentRequest>
   </soapenv:Body>
</soapenv:Envelope>

Code:

[HttpPost("TestParsian")]
public async Task TestParsian([FromBody] PaymentRequest request)
{
    ParsianSales.SaleServiceSoapClient.EndpointConfiguration endpointConfiguration;
    endpointConfiguration = ParsianSales.SaleServiceSoapClient.EndpointConfiguration.SaleServiceSoap12;
    var srv = new ParsianSales.SaleServiceSoapClient(endpointConfiguration);

    #region
    var binding = new BasicHttpBinding();
    binding.Security.Mode = BasicHttpSecurityMode.Transport;
    binding.Security.Transport.ClientCredentialType = HttpClientCredentialType.None;

    srv.Endpoint.Binding = binding;
    #endregion

    System.Net.ServicePointManager.ServerCertificateValidationCallback += (sender, cert, chain, sslPolicyErrors) => { Console.WriteLine("ssl"); return true; };

    ParsianSales.ClientSaleRequestData saleRequest = new()
    {
        LoginAccount = request.LoginAccount,
        Amount = request.Amount,
        Originator = request.Originator,
        OrderId = (long)Convert.ToDouble(request.OrderId),
        CallBackUrl = request.CallBackUrl
    };

    Console.WriteLine("before");
    var result = srv.SalePaymentRequest(saleRequest);
    Console.WriteLine(result.Message);
    Console.WriteLine(result.Token);
}

Troubleshooting Steps Taken:

I have tried setting the TLS protocol version:

System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls12;

I configured the server to accept the certificate.

I tested the code in a loop to see if retrying would succeed, but the problem persists.

I should also note that sometimes when I execute the request in SoapUI, it either fails or takes a long time to complete, while my code doesn’t receive a response at all.