Troubleshooting 404 Error on HTTPS POST Request in WCF Service Application

Question

I'm facing a 404 error when making HTTPS POST requests to my WCF Service Application. Interestingly, HTTPS GET requests and metadata retrieval work fine. Here's a brief overview of my setup:

Web.config: Includes standard diagnostics, service behaviors enabling HTTPS, and basic HTTP bindings with Transport security mode. Global.asax.cs: Basic setup with CORS headers, and a special condition for HTTP OPTIONS method. Relevant Configurations:

Web.config

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <system.diagnostics>
    <sources>
      <source name="System.ServiceModel" switchValue="Information, ActivityTracing">
        <listeners>
          <add name="traceListener" type="System.Diagnostics.XmlWriterTraceListener" initializeData="trace.log" />
        </listeners>
      </source>
    </sources>
  </system.diagnostics>
  <appSettings>
    <!--Settings-->>
  </appSettings>
  <connectionStrings />
  <system.web>
    <compilation debug="true" targetFramework="4.6.2" />
    <pages controlRenderingCompatibilityVersion="4.0" />
  </system.web>
  <system.serviceModel>
    <bindings>
      <basicHttpBinding>
        <binding name="BasicHttpBinding_IserviceB">
          <security mode="Transport">
            <transport clientCredentialType="None" />
          </security>
        </binding>
        <binding name="BasicHttpBinding_IserviceA">
          <security mode="Transport">
            <transport clientCredentialType="None" />
          </security>
        </binding>
      </basicHttpBinding>
    </bindings>
    <client>
      <endpoint address="http://10.100.31.54:8043/serviceA.svc" binding="basicHttpBinding" bindingConfiguration="BasicHttpBinding_IserviceA" contract="serivceA.IserviceA" name="BasicHttpBinding_IserviceA" />
      <endpoint address="http://localhost:8081/serviceB.svc" binding="basicHttpBinding" bindingConfiguration="BasicHttpBinding_IserviceB" contract="serviceB.IserviceB" name="BasicHttpBinding_IserviceB" />
    </client>
    <behaviors>
      <serviceBehaviors>
        <behavior>
         <serviceMetadata httpGetEnabled="true" httpsGetEnabled="true" />
          <serviceDebug includeExceptionDetailInFaults="true" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <serviceHostingEnvironment multipleSiteBindingsEnabled="true" />
  </system.serviceModel>
  <system.webServer>
    <modules runAllManagedModulesForAllRequests="true" />
  </system.webServer>
  <runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <!--Assemblies-->
    </assemblyBinding>
  </runtime>
</configuration>

Global.asax.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.SessionState;
using System.Web.Routing;
using System.ServiceModel.Activation;
using InvoiceWebService;

namespace InvoiceService
{
    public class Global : System.Web.HttpApplication
    {
        protected void Application_BeginRequest(object sender, EventArgs e)
        {
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Origin", "*");
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Methods", "*");
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Headers", "*");
            HttpContext.Current.Response.AddHeader("Access-Control-Expose-Headers", "*");

            if (HttpContext.Current.Request.HttpMethod == "OPTIONS")
            {
                HttpContext.Current.Response.End();
            }
        }

    }
}

I've ensured that my service metadata is accessible over HTTPS, and GET requests are successful. However, POST requests consistently return a 404 error. I've checked the endpoint configurations and tried various clientCredentialType settings without success.

What could be causing this 404 error on POST requests over HTTPS, and how can I resolve it?

Thank you for any insights or suggestions!