In the Validation Rules I would like to have custom functions, we can do that in Zoho CRM and its really useful 

There are some custom fields in Sales Orders and Purchase Order Modules

We are using Zoho Books With our internal apps, and we need to put some data from our app to Sales Order and Purchase Order 

But there have been many instances where an team member entered the wrong data 

I would like the ability to call a custom function from Validation Rule and I can make API calls to our app and verify the data before saving