I am using a UE script to do some extra work when saving a JE. But, if there is a missing value I want to prevent the record from creating. I am using the UE to modify but the save call is happening in another script. How can I prevent saving from within the UE?

This sounds like what the saveRecord entry point in a client script is intended for. https://system.na3.netsuite.com/app/help/helpcenter.nl?fid=section_4410693749.html

@jarens thanks, i'll try that

Also, if the JE is being created via another process like ARM or Fixed Asset Depreciation, you might try throwing an error in a beforeSubmit.