N/error Module
UserEventError.cause
Property Description: The cause of the error.
Type: string (read-only)
Supported Script Types: User event scripts For more information, see SuiteScript 2.0 User Event Script Type.
Module: N/error Module
Since: 2015.2
Search NetSuite - https://system.netsuite.com/app/help/helpcenter.nl?search=UserEventError.cause

// Code Example 1

//Add additional code

//...

var UEcustom_error = error.create({

    name: 'MY_ERROR_CODE',

    message: 'my custom UserEventError details',

    cause: 'the cause of the error',

    notifyOff: false

});

log.debug("Error cause: " + UEcustom_error.cause); // 'Error cause: ' followed by the cause will be logged

 ...

//Add additional code



//SOURCE: https://system.netsuite.com/app/help/helpcenter.nl?fid=section_158049435042.html