Long FormUrlEncodedContent

gistfile1.txt

//IEnumerable<KeyValuePair<string, string>> serializedParameters
      // Do this instead of using FormUrlEncodedContent as it only supports url escaping of strings shorter than 30,000 (or 60,000)
      // Would use MultipartFormDataContent but Esri doesn't look like it accepts that
      var pars = string.Join("&", serializedParameters.Select(p => p.Key + "=" + Encode(p.Value)));
      var content = new ByteArrayContent(Encoding.ASCII.GetBytes(pars));
      content.Headers.ContentType = new MediaTypeHeaderValue("application/x-www-form-urlencoded");
      
      var message = await client.PostAsync(url, content);
      return await message.Content.ReadAsStringAsync();


private static string Encode(string value)
{
  if (value == null)
      return null;

  if (value.Length < 32000)
      return Uri.EscapeDataString(value);

  return string.Concat(
      value
      .Split(32000)
      .Select(c => Uri.EscapeDataString(new string(c.ToArray())))
  );
}