HttpClientFactory returns results of previous request

Question

I have an ASP.NET Core Web API service built using .NET 6 that makes http requests using C# HttpClientFactory to external services.

The issue I am facing is that the second request with different arguments returns same result as for the previous request.

I tried clearing default headers at the start of every request no luck.

What worked for me:

1. RestSharp: https://restsharp.dev/
2. Using new HttpClient() instance instead of httpClientFactory.CreateClient()

I would like to make it work with httpClientFactory as this is the recommended way. Any thoughts why much appreciated.

// Each request has different access token but same body
public async Task<MyResponse> GetXyz(object requestBody, string accessToken)
{
    var uri = "...";
    return await this.httpClientFactory.CreateClient("GetXyz").PostAsync<MyResponse>(uri, requestBody, GetHeaders(accessToken));
}

private static IList<(string, string)> GetHeaders(string accessToken)
{
    var headers = new List<(string, string)>
    {
        (HeaderNames.Accept, "application/json"), 
    };

    if (!string.IsNullOrWhiteSpace(accessToken))
    {
        headers.Add((HeaderNames.Authorization, "Bearer " + accessToken));
    }

    return headers;
}

public static async Task<T> PostAsync<T>(this HttpClient httpClient, string uri, object data, IList<(string, string)> headers = null)
    where T : class
{
    // httpClient.DefaultRequestHeaders.Clear();

    var body = data.Serialise(); // convert to JSON string
    
    using (var request = new HttpRequestMessage(HttpMethod.Post, uri))
    {
        request.AddRequestHeaders(headers);
        request.Content = new StringContent(body, Encoding.UTF8, "application/json");

        using (var httpResponse = await httpClient.SendAsync(request))
        {
            var jsonResponse = await httpResponse.Content.ReadAsStringAsync();
            return JsonSerializer.Deserialize<T>(jsonResponse);
        }
    }
}

EDIT 2: NETWORK TRAFFIC DIFF

Using Fiddler Classic with basic client httpclientfactory.CreateClient() here are the diffs between 2 requests headers that suffer from the issue: