Here is the correct way to send POST using HTTP Client.csharpcode, .csharpcode pre { font-size: 13.3333px; font-width: 400; color: black; font-family: "Courier New"; } .csharpcode pre { margin: 0px; } .csharpcode .comment { color: #008000; } .csharpcode .comment2 { color: #808080; } .csharpcode .type { color: #2B91AF; } .csharpcode .keyword { color: #0000FF; } .csharpcode .string { color: #A31515; } .csharpcode .preproc { color: #0000FF; } var client = new HttpClient(); var postData = new List<KeyValuePair<string, string>>();...