Can’t redirect to another action method after form submission

I want to redirect to an action that says Order is successful, but when the form is submitted, it redirects to the same action /Checkout with error: This page isn't working. This is understandble since the query strings are not present, but this doesn’t matter to me. I want
it to redirect to /OrderComplete instead. The debugger confirmed ModelState is valid and RedirectToAction is hit every time.

These are the get and post action methods.

public async Task<IActionResult> Checkout(string vendorId, int skillId)
{
    var skill = await _skillRepository.GetSkillById(skillId);
    OrderViewModel OrderView = new OrderViewModel
    {
        ApplicationUserId = vendorId,
        ServiceType = skill.SkillType
    };
    return View(OrderView);
}

[HttpPost]
[ValidateAntiForgeryToken]
public IActionResult Checkout(OrderViewModel orderViewModel)
{
    if (ModelState.IsValid)
    {
        _orderRepository.CreateOrder(orderViewModel);
        return RedirectToAction("OrderComplete");
    }
    return View(orderViewModel);
}

This is the form action in view.

<form asp-action="Checkout" method="post">

Note: ApplicationUserId and ServiceType are hidden fields that
are filled before posting the form.

Update

After commenting out this line _orderRepository.CreateOrder(orderViewModel);, it redirected successfully. So, the problem seems to be coming from this method CreateOrder.

public class OrderRepository : IOrderRepository
{
    private readonly QuickServiceDbContext _context;
    private readonly IMapper _mapper;
    public OrderRepository(QuickServiceDbContext context, IMapper mapper)
    {
        _context = context;
        _mapper = mapper;
    }
    public void CreateOrder(OrderViewModel orderViewModel)
    {
        Order order = _mapper.Map<Order>(orderViewModel);
        _context.Orders.Add(order);
        //_context.Users
        _context.SaveChangesAsync();
    }
}

Answers:

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Method 1

Changing _context.SaveChangesAsync() to:

_context.SaveChanges();

fixed the issue. I don’t understand why this is yet, but I should never have spent so much time on an issue so trivial. Any insight into why SaveChangesAsync() was preventing a redirection would be appreciated.

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