ASP.NET Core Web API app returning JSON instead of XML

Why is my ASP.NET Core Web API app not returning XML? It is always returning JSON. When I specify "[Produces("application/xml")]" attribute in my controller, it returns a 406 status code:

Link to screenshot

Here is my controller code:

using GlobalWarmingCenter.Data;
using GlobalWarmingCenter.Models;
using Microsoft.AspNetCore.Antiforgery;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using System.Threading.Tasks;

// For more information on enabling MVC for empty projects, visit https://go.microsoft.com/fwlink/?LinkID=397860

namespace GlobalWarmingCenter.Controllers
{
    [Route("api/[controller]")]
    public class DimCustomerController : Controller
    {
        private readonly PointOfContact _pointOfContact;
        private readonly AdventureWorksDW2012Context _context;
        private readonly ILogger _logger;
        private readonly IAntiforgery _antiforgery;

        public DimCustomerController(AdventureWorksDW2012Context context,
            ILogger<DimCustomerController> logger,
            IOptions<PointOfContact> PointOfContact,
            IAntiforgery antiforgery)
        {
            _context = context;
            _logger = logger;
            _pointOfContact = PointOfContact.Value;
            _antiforgery = antiforgery;
        }

        [HttpGet]
        public IActionResult Get()
        {
            var tokens = _antiforgery.GetAndStoreTokens(HttpContext);

            return new ObjectResult(new
            {
                token = tokens.RequestToken,
                tokenName = tokens.HeaderName
            });
        }

        // GET: /<controller>/
        public IActionResult Index()
        {
            return View();
        }

        [HttpPost("{maritalstatus}")]
        [ValidateAntiForgeryToken]
        [Produces("application/xml")]
        public async Task<IActionResult> Index(
        [Bind("MaritalStatus")]
        DimCustomer dimcustomer)
        {
            try
            {
                DimCustomer[] result = null;
                if (ModelState.IsValid)
                {
                    var something = dimcustomer.MaritalStatus;
                    result = await _context.DimCustomer.FromSql("usp_GetAllDimCustomer @p0", dimcustomer.MaritalStatus).ToArrayAsync();
                }
                var tokens = _antiforgery.GetAndStoreTokens(HttpContext);

                //  return new OkObjectResult(tokens);

                return Ok(result);
            }
            catch (DbUpdateException ex)
            {
                //Log the error (uncomment ex variable name and write a log.
                ModelState.AddModelError("", ex.Message);
                ModelState.AddModelError("", "Unable to save changes. " +"Try again, and if the problem persists, " +"contact me at " + _pointOfContact.EmailAddress + ".");
                return View();
            }
        }
    }
}

I added the XML serializer formatters to my Startup.cs file:

services.AddMvc().AddXmlSerializerFormatters();

When I remove the "[Produces("application/xml")]" attribute from my controller, it returns JSON. However, I put "Accept: application/xml" and "Content-Type: application/xml" in my headers, as you can see in the screenshot (link provided above).

Thanks!