send an openai prompt in csharp

main.cs
using System;
using System.Net.Http;
using System.Text.Json;
using System.Threading.Tasks;

class Program
{
    static async Task Main(string[] args)
    {
        var prompt = "Once upon a time";
        var apiKey = "your-api-key";
        var apiUrl = "https://api.openai.com/v1/engines/davinci-codex/completions";

        var httpClient = new HttpClient();
        httpClient.DefaultRequestHeaders.Add("Authorization", $"Bearer {apiKey}");

        var requestBody = new {
            prompt = prompt,
            max_tokens = 10,
            n = 1,
            stop = "."
        };

        var requestBodyJson = JsonSerializer.Serialize(requestBody);
        var httpContent = new StringContent(requestBodyJson, System.Text.Encoding.UTF8, "application/json");

        var httpResponse = await httpClient.PostAsync(apiUrl, httpContent);
        var httpResponseContent = await httpResponse.Content.ReadAsStringAsync();
        var responseObject = JsonSerializer.Deserialize<OpenAiResponse>(httpResponseContent);

        Console.WriteLine(responseObject.choices[0].text);
    }
}

class OpenAiResponse
{
    public OpenAiChoice[] choices { get; set; }
}

class OpenAiChoice
{
    public string text { get; set; }
    public double logprobs { get; set; }
    public int finish_reason { get; set; }
}
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