Answer
Temporarily add a simple blocking error message to an Execute Online SQL-type action on the event — for example, ERROR_SYS.record_general('', 'ERR: Test Error from Custom Event') — then make the change that should trigger the event. If the event is genuinely firing, that test error will pop up immediately; if nothing appears, the event itself isn't triggering, which tells you to focus troubleshooting on the event's trigger conditions rather than the action logic. Remove the test error message once you've confirmed triggering behavior and move on to validating the real action.