C# - Can't get this seemingly simple web request working

Question

I have the following powershell Web-Request that works correctly for sending a command to a PTZ camera:

Invoke-WebRequest -UseBasicParsing -Uri "http://192.168.111.75/ajaxcom" `
-Method "POST" `
 -Headers @{
 "Accept"="application/json, text/javascript, */*; q=0.01"
   "Accept-Encoding"="gzip, deflate"
   "Accept-Language"="en-US,en;q=0.9"
   "DNT"="1"
   "Origin"="http://192.168.111.75"
   "X-Requested-With"="XMLHttpRequest"
 } `
 -ContentType "application/x-www-form-urlencoded; charset=UTF-8" `
 -Body "szCmd=encodedStringHere"

I'm trying to recreate this in C# but I can't seem to get it to work..

I've tried a whole bunch of stuff but this is what my code looks like right now:

 public async static void Execute()
{
    using HttpClient client = new HttpClient();
    
   // client.DefaultRequestHeaders.Accept.Add(
   //     new MediaTypeWithQualityHeaderValue("application/json, text/javascript, */*; q=0.01"));
   // client.DefaultRequestHeaders.AcceptEncoding.Add(new StringWithQualityHeaderValue("gzip, deflate"));
   // client.DefaultRequestHeaders.AcceptLanguage.Add(new StringWithQualityHeaderValue("en-US,en;q=0.9"));
    client.DefaultRequestHeaders.Add("DNT", "1");
    client.DefaultRequestHeaders.Add("Origin", "http://192.168.111.75");
    client.DefaultRequestHeaders.Add("X-Requested-With", "XMLHttpRequest");
    string stringData = "{\"SysCtrl\":{\"PtzCtrl\":{\"nChanel\":0,\"szPtzCmd\":\"right_start\",\"byValue\":50}}}";
    var data = Encoding.Default.GetBytes(stringData);
    KeyValuePair<string, string> kvp = new KeyValuePair<string, string>("Body", data.ToString());
    var content = new FormUrlEncodedContent(new[] { kvp });
    var response = await client.PostAsync("http://192.168.111.75/ajaxcom", content);
    var responseString = await response.Content.ReadAsStringAsync();
}

I don't know why I'm having so much trouble with this, any help is appreciated