how to call PostAsyn

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WebAPI

My web api is as bellow

public class MultibuysController : ApiController
    
        private const int DEFAULT_TIMEOUT = 2000;
        readonly IMultibuyService _multibuyService;

        public MultibuysController()
        {
            _multibuyService = new MultibuyService();
        }

        public MultibuysController(IMultibuyService multibuyService)
        {
            _multibuyService = multibuyService;
        }

        // GET api/multibuys/1234560101
        public Discounts Get(string id, int timeout = DEFAULT_TIMEOUT)
        {
            return _multibuyService.GetMultibuyItemDiscount(id, timeout);
        }

        // POST api/multibuys
        public Discounts Post(Bag bag, int timeout = DEFAULT_TIMEOUT)
        {
            return _multibuyService.GetMultibuyItemDiscount(bag, timeout);
        }
    }

from my client website i call the api get method
as bellow

public Discounts AllItems(string id)
        {
            List<Product> list = new List<Product>();
            Bag _discountedBag = new Bag();
            HttpClient client = new HttpClient();
            client.BaseAddress = new Uri("http://localhost:56835/");       
            // Add an Accept header for JSON format.
            client.DefaultRequestHeaders.Accept.Add(
                new MediaTypeWithQualityHeaderValue("api/multibuys"));
        
            HttpResponseMessage response = client.GetAsync("api/multibuys/Get?id=?" + id).Result;
          
            if (response.IsSuccessStatusCode)
            {
                 return response.Content.ReadAsAsync<Discounts>().Result;
                 
            }
          

            return new Discounts();
        }

now i wanted to create a method to call the post method from my client web
but now sure how to use the PostAsyn could some one help me to on this plz
what i want is

public Discounts PostABag(Bag bag)
        {
            HttpClient client = new HttpClient();
            client.BaseAddress = new Uri("http://localhost:56835/"); 
            HttpResponseMessage response = client.PostAsync("api/multibuys/Post?bag=?"

	//need help to finish off this function 
        }

appreciate all your help