Form personalization in AP invoice form when save

Hi,

I want to update a value in one of the invoice header attribute and hence configured a form personalization as mentioned below;

Trigger event : WHEN VALIDATE RECORD

Trigger object : INV_SUM_FOLDER

Condition : INV_SUM_FOLDER.SOURCE = 'ERS'

Processing mode : Both

Actions:

Object type : Item

Target object : INV_SUM_FOLDER.ATTRIBUTE5

property : Value

Value = 9999

The above works, when i validate in personalization form. But, while saving the invoice record it is not working.

The value has to be updated in the attribute5 when save the record. What is the correct trigger object to be updated? Any idea please share.