Error calling API Endpoint

Can anyone help me spot what’s wrong with this C# code? I get the error:
Exception Caught! Message :{0} Response status code does not indicate success: 404 (Not Found). The endpoint works in Postman

public async Task<string> Send35Prompt(string strPrompt)
{
  var responseBody = "";
  HttpClient client = new HttpClient();
  var apiKey = "MY KEY"; 
  var endpoint = "https://api.openai.com/v1/chat/completions/";
  var jsonString = strPrompt;
  try
  {
    var content = new StringContent(strPrompt.Replace('\'', '\"'), Encoding.UTF8, "application/json");
    client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", apiKey);
    var response = await client.PostAsync(endpoint, content);
    response.EnsureSuccessStatusCode();
    responseBody = await response.Content.ReadAsStringAsync();

    // responseBody will contain the JSON response from the API
    Console.WriteLine(responseBody);
  }
  catch (HttpRequestException e)
  {
    responseBody = "\nException Caught! " + "Message :{0} " + e.Message;
    //Console.WriteLine("Message :{0} ", e.Message);
  }
  return responseBody;
}