I'm using Zoho books and creating Estimates and Invoices. Customers have vehicles that we service. Is it possible to have a related list of vehicles that can be selected when creating the Estimate? 

Here's what I've done so far: 

1. Created a Form in Zoho Creator that simply stores the Vehicles and has a field with Zoho Books Contact Id. 

2. In Estimate Settings, I created a Related Lists deluge script to getRecords from Form, using the Contact Id to get list of vehicles for the specific Contact.  

3. Verified that I am able to see the Related List data as intended. 

However, I'm only able to see the Related List data when the Estimate is viewed, not when edited. I tried creating Custom Fields in the Estimate but they are only text entry fields . Ideally, I would need a drop-down selection with the list of Related List items for the Contact selected. Is this possible?