Zoho Invoice custom function for Estimate module

Zoho Invoice custom function for Estimate module

Hi!
I using invoice.zoho.
I want to update "quantity" after push custom fields (Ex: NightQty and Qly): 
  1. quantity = NightQty * Qly
I created a custom function for Estimate module in Custom functions tab:
  2. estimateID = estimate.get("estimate_id");
  3. organizationID = organization.get("organization_id");
  4. estimateMap = zoho.books.getRecordsByID("Estimates",organizationID,estimateID).get("estimate").toMap();
  5. itemJSON = estimateMap.get("line_items").toList();
  6. updatedLineItems = List();
  7. for each  item in itemJSON
  8. {
  9. item_CFs = item.get("item_custom_fields").toList();
  10. updatedLineItem = Map();
  11. updatedLineItem.put("line_item_id",item.get("line_item_id"));
  12. nights = 0;
  13. roomqty = 0;
  14. for each  item_cf in item_CFs
  15. {
  16. if(item_cf.get("label").equalsIgnoreCase("NightQly"))
  17. {
  18. nights = item_cf.get("value").toDecimal();
  19. }
  20. else if(item_cf.get("label").equalsIgnoreCase("Qly"))
  21. {
  22. roomqty = item_cf.get("value").toDecimal();
  23. }
  24. }
  25. qty = nights * roomqty;
  26. updatedLineItem.put("quantity",qty);
  27. updatedLineItems.add(updatedLineItem);
  28. }
  29. json = Map();
  30. json.put("line_items",updatedLineItems);
  31. response = zoho.books.updateRecord("Estimates",organizationID,estimateID,json);
  32. info response.get("message");
And I added to "Workflow Rules". But this function not working and I receive error:  Custom Function Estimate failed to execute for the workflow Update Estimate.  
This code worked on Invoice module with "zoho intergration" like "zoho.invoice.getRecordByID()" and "zoho.invoice.update()".
Can help me?