Is there a way to put a constraints in the Journal Event Handler rule? For example, can you create an error message to prompt the user if they try to submit a Journal with Account IsIC=True, and IC None.

It is recommended to use the constraints on the account members, or you can utilize a "No Input" rule that is specific for O#Adj.

NOTE: There are some 5.X versions where this was a known issue whereby constraints were not being applied upon journal postings. It is believed that the customer involved here was on one of these versions. 

 

Source: Office Hours 2020-09-27 Partner Enablement