How can I successfully send http requests to my ASP.NET Core controller

I have built a .NET Core server that is linked up to a postgres database but what I'm attempting to do now is send requests to the server from a mobile app to execute the CRUD functions with the server. This is so the mobile can send requests that will be an object using a model that's setup in both server and mobile app to be the same. Then the server will POST that request to the database.

This code is on the mobile app that makes a baseAddress for the server and then the other code is inside a save method that turns the object into json string and presumably sends it to the controller.

private static readonly HttpClient sharedClient = new()
        {
            BaseAddress = new Uri("http://10.188.144.18:5240/AandEBacklog"),
        };

using StringContent jsonContent = new(JsonSerializer.Serialize(new { note }),
                Encoding.UTF8,
                "application/json");

using HttpResponseMessage response = await sharedClient.PostAsync("MobileResponse", jsonContent);

I know that I need to do something with routing in the program.cs file in the server

app.UseHttpsRedirection();
app.UseAuthorization();
app.MapControllers();

I have a controller that connects to the database but don't know weather I can use the httpRequest in that controller or if I need to send it to another one and then the other controller handles it

using Microsoft.AspNetCore.Mvc;
namespace delamainServer.Controllers;

[ApiController]
[Route("[controller]")]
public class AandEBacklogController : ControllerBase
{
    //CONNECTING TO DATABASE.
    private readonly DataContext context;

    //var httpRequest = HttpContext.Request;

    public AandEBacklogController(DataContext context)
    {
        this.context = context;
    }

    //post method example to add entry
    [HttpPost]
    public async Task<ActionResult<List<AandEBacklog>>> Addemrgncy(AandEBacklog booking)
    {
        context.AandEBacklogs.Add(booking);
        await context.SaveChangesAsync();

        return Ok(await context.AandEBacklogs.ToListAsync());
    }
}

Many thanks in advance

For client part:

    var client = new HttpClient() { BaseAddress = new Uri("http://10.188.144.18:5240") };
    var content = new StringContent("yourJsonString", Encoding.UTF8, "application/json");
    var response = await client.PostAsync("/AandEBacklog", content);
    var responseString = await response.Content.ReadAsStringAsync();

EDIT:
Let's setup simple GET endpoint:

[ApiController]
[Route("[controller]")]
public class TimeController : ControllerBase
{
    public ActionResult<string> GetCurrentTime() => $"{DateTime.Now}";
}

Verify it works from browser (e.g. http://localhost:5000/Time).
If it works try client from console or Xamarin app:

var client = new HttpClient() { BaseAddress = new Uri("http://localhost:5000") };
var response = await client.GetAsync("/Time");
var content = await response.Content.ReadAsStringAsync();
Console.WriteLine(content);