This event will be fired when something goes wrong while backing up.
It has two public properties:
$exception: an object that extends PHP's Exception class. 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 zipping the files. If it's an instance of Spatie\Backup\BackupDestination\BackupDestination then something went wrong copying the zip over to the backup destination.
This event will be fired right after the zipfile - containing the dumps of the databases and any files that were selected for backup - is created, and before that zip will get copied over to the backup destination(s). You can use this event to do last minute manipulations on the created zip file.
It has one public property $pathToZip which contains a path to the created zipfile.