test.cs

[HttpPost]
public string PromptRequest([FromBody] ChatGPTRequest request)
{

    var htmlSuffix = ". Create the results in formatted HTML format with h1, p and li elements.";

    // Remove a trailing full stop, if present
    if (request.Text.EndsWith("."))
    {
        request.Text = request.Text.TrimEnd('.');
    }

    HttpClient client = new HttpClient
    {
        DefaultRequestHeaders =
        {
            Authorization = new AuthenticationHeaderValue("Bearer", Models.Constants.OPENAI_API_KEY)
        }
    };

    Request apiRequest = new Request
    {
        Messages = new[]
        {
            new RequestMessage
            {
                 Role = "system",
                 Content = "You are a helpful assistant."
            },
            new RequestMessage
            {
                 Role = "user",
                 Content = request.Text + htmlSuffix
            }
        }
    };

    StringContent content = new StringContent(
        System.Text.Json.JsonSerializer.Serialize(apiRequest),
        Encoding.UTF8,
        "application/json"
    );

    HttpResponseMessage httpResponseMessage = client.PostAsync(
        "https://api.openai.com/v1/chat/completions",
        content
    ).Result;

    if (httpResponseMessage.IsSuccessStatusCode)
    {
        Response response = System.Text.Json.JsonSerializer.Deserialize<Response>(
            httpResponseMessage.Content.ReadAsStringAsync().Result
        );

        var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(response.Choices[0].Message.Content);
        return System.Convert.ToBase64String(plainTextBytes);
    }

    return null;
}