if not order.is_complete:
				order_total = order.order_total
				nonce = request_data.get("payment_method_nonce")
				if nonce:
					result = braintree.Transaction.sale({
					    "amount": order_total,
					    "payment_method_nonce": nonce,
					    "billing": {
						    "postal_code": "%s" %(order.billing_address.zipcode),

						 },
					    "options": {
					        "submit_for_settlement": True
					    }
					})
					success = result.is_success
					if success:
						#result.transaction.id to order
						order.mark_completed(order_id=result.transaction.id)
						#order.mark_completed(order_id="abc12344423")
						order.cart.is_complete()
						response["message"] = "Your order has been completed."
						response["final_order_id"] = order.order_id
						response["success"] = True
					else:
						#messages.success(request, "There was a problem with your order.")
						error_message = result.message
						#error_message = "Error"
						response["message"] = error_message
						response["success"] = False
			else:
				response["message"] = "Ordered has already been completed."
				response["success"] = False

class Cart(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL, null=True, blank=True, on_delete=models.CASCADE)
    timestamp = models.DateTimeField(auto_now_add=True, auto_now=False)
    updated = models.DateTimeField(auto_now_add=False, auto_now=True)

class CartItem(models.Model):
    cart = models.ForeignKey(Cart, on_delete=models.CASCADE)
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    quantity = models.PositiveIntegerField(default=1)
    # line_item_total also i could not understand.
    line_item_total = models.DecimalField(max_digits=10, decimal_places=2)