This event is fired when something goes wrong while cleaning up.
It has two public properties:
$exception: an object that conforms to the Exception interface. It is highly likely that $exception->getMessage() will return more information on what went wrong.
$backupDestination: if this is null then something probably went wrong before even connecting to one of the backup destinations. If it is an instance of Spatie\Backup\BackupDestination\BackupDestination something went wrong when trying to connect or
write to that destination.