I want to send requests to the API from the UI with Blazor .Net Core

This is how I do on the UI:

@code {

    OrderDto orderDto = new();

    protected override async Task OnInitializedAsync()
    {
        var urlString = "myUrlString";
        var orderListResponse = await urlString.PostJsonAsync(orderDto);
    }   
}

And that’s my API part:

[Route("getOrderList")]
[HttpPost]
public async Task<ActionResult<List<OrderDto>>> GetOrderList(OrderDto orderDto) 
{           
    var response = await _orderService.OrderList(orderDto);
    return response;
}

I can get the data from _orderService but when I come to flurl’s response, I get the 500 error and I don’t understand why it gives this error.