send POST request to Microsoft web browser

To create a POST request you have to use the HTTPWebRequest class. The Request method has to be set to POST. You have to define the content type (text, xml or anything based on your requirement) and finally write the data that you need to send to the server in the stream of the Request object.
Refer the code below -

You have to write your data that you need to send in the message body of your POST request in the str string. This can be c# class, or simple string separated by '&' as per your need.

// Convert string data into byte array 
byte[] dataByte = Encoding.UTF8.GetBytes(strData);
            
            HttpWebRequest POSTRequest = (HttpWebRequest)WebRequest.Create(strURL);
            POSTRequest.Method = "POST";
// Set the content type - Mine was xml.
            POSTRequest.ContentType = "text/xml";
            POSTRequest.KeepAlive = false;
            POSTRequest.Timeout = 5000;
            POSTRequest.ContentLength = dataByte.Length;
// Get the request stream
            Stream POSTstream = POSTRequest.GetRequestStream();
            // Write the data bytes in the request stream
            POSTstream.Write(dataByte, 0, dataByte.Length); 

//Get response from server
            HttpWebResponse POSTResponse = (HttpWebResponse)POSTRequest.GetResponse();

Hope this helps