Enable CORS preflight ASP.NET on IIS

First you have to make sure you have successfully installed the cors module, then you need to add the following configuration in the web.config of the application:

 <system.webServer> 
   <cors enabled="true">
    <add origin="*" allowed="true" />
  </cors>
  </system.webServer>

This configuration node is under the configuration node.

If it is still not resolved, you can also solve the cross-domain problem by adding the following code to the Global file:

protected void Application_BeginRequest(object sender, EventArgs e)
        {
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Origin", "*");

            if (HttpContext.Current.Request.HttpMethod == "OPTIONS")

            {
                HttpContext.Current.Response.AddHeader("Access-Control-Allow-Methods", "*");

                HttpContext.Current.Response.AddHeader("Access-Control-Allow-Headers", "*");

                HttpContext.Current.Response.End();
            }

        }