public async Task <IActionResult> Delete(int id)
        {
            if (ModelState.IsValid)
            {
                var cbill = _repository.GetCustomBill(id);
                if (cbill == null)
                {
                    return(BadRequest("Custom bill does not exist."));
                }
                _repository.DeleteCustomBill(cbill);

                if (await _repository.SaveChangesAsync())
                {
                    return(Ok($"api/custombills/"));
                }
            }
            return(BadRequest("Failed to delete the custom bill."));
        }