OrderItems and OrderTaxLines are ienumerables, to be displayed in grids. there is no, to my knowledge, awaitable functions to get them. I don't see what else could be the problem
protected override async Task OnParametersSetAsync(){ if (Order != null) { OrderItems = db.OrderItems.Include(o => o.Product).Include(o => o.productSubChoice).Where(c => c.Status != Status.Deleted && c.OrderID == Order.ID); if (Order.OrderStatusID == InProgressStatusID) await Order.UpdatePriceList(db); await UpdateTaxesLines(); OrderSubTotal = OrderItems.Sum(i => i.TotalPrice); OrderTotal = OrderSubTotal + OrderTaxLines.Sum(t => t.Value); }}public async Task UpdateTaxesLines(){ OrderTaxLines = db.OrderTaxLines.Include(t => t.Tax).Where(c => c.Status != Status.Deleted && c.OrderID == Order.ID);}