From the https://editor.datatables.net/reference/event/submitError documentation for the submitError event, the description states:
"This is fired when data has been submitted to the server but an error occurred on the server, not a validation in data error, but an error in the processing of the data (typically a JSON formatting error)."
The documentation states this event is not for validation in data error, but there is no reference to which event should be used for validation in data error. None of the other supplied events seem to fit the need either.