Here's a C# conversion of your JavaScript function. This translation aims to maintain the same logic and structure as the original JavaScript function while adapting it to C# syntax and idioms.
```csharp
using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Text;
using Newtonsoft.Json;
public class PlayStreamHandler
{
private static readonly string DiscordWebhookURL = "----";
private static readonly


