code: func (ctrl Controller) Complete(w http.ResponseWriter, req *http.Request) {
  	req.ParseForm()
  
  	order := getCurrentOrder(w, req)
  	if order.AmazonOrderReferenceID = req.Form.Get("amazon_order_reference_id"); order.AmazonOrderReferenceID != "" {
  		order.AmazonAddressAccessToken = req.Form.Get("amazon_address_access_token")
  		tx := utils.GetDB(req)
  		err := orders.OrderState.Trigger("checkout", order, tx, "")
  
  		if err == nil {
  			tx.Save(order)
  			http.Redirect(w, req, "/cart/success", http.StatusFound)
  			return
  		}
  		utils.AddFlashMessage(w, req, err.Error(), "error")
  	} else {
  		utils.AddFlashMessage(w, req, "Order Reference ID not Found", "error")
  	}
  
  	http.Redirect(w, req, "/cart", http.StatusFound)
  }
docs: // Complete complete shopping cart