httpclient call is invoked after await keyword in dotnet core - asynchronous

Question

I would like to do some operation which doesn't depend on API response and at the same time I want API to finish its process.
But in my case, API doesn't receive request when postasync is executed.
Instead, Web api receive request after await weatherForeCastdata.
I noticed strange behavior today
when I executed endpoint for first time(both the apis), webapi received request after postasync method. From second time, api receives request after executing await weatherForeCastdata.
I launched applictaion from vs code
browser : chrome
Can anyone help me ?
public async Task<IEnumerable<WeatherForecast>> Get()
{
var rng = new Random();
var weatherForeCastdata = new HttpClientCall<WeatherForecast>(_configuration).PostRequest(_configuration["Services:Payperiod"],new WeatherForecast());
Console.WriteLine("apiinvoked");
var data = await weatherForeCastdata;
//var data1 = await data.Content.ReadAsStringAsync();
return JsonConvert.DeserializeObject<IEnumerable<WeatherForecast>>(data);
}
public class HttpClientCall<T> where T : class
{
HttpClientHandler httpClientHandler = new HttpClientHandler();
private readonly IConfiguration _configuration;
internal HttpClientCall(IConfiguration configuration)
{
httpClientHandler = new HttpClientHandler();
httpClientHandler.ServerCertificateCustomValidationCallback = (message, cert, chain, sslPolicyErrors) =>
{
if (sslPolicyErrors == SslPolicyErrors.None)
{
return true; //Is valid
}
return true;
};
_configuration = configuration;
}
public async Task<string> PostRequest(string apiUrl, T postObject)
{
using (var client = new HttpClient(httpClientHandler))
{
client.DefaultRequestHeaders.Add("ClientId", _configuration["header"]);
Console.WriteLine(apiUrl);
var response = client.PostAsync(apiUrl, postObject, new JsonMediaTypeFormatter());
var response1=await response;
return await response1.Content.ReadAsStringAsync();
}
}
}