backup problem (WPvivid plugin)

while i try to backup my website with wpvivid plugin , it keeps throwing this error :

” Backup error: A exception (Exception) occurred Output file is not writable (Code: 0, line 135 in /code/wp-content/plugins/wpvivid-backuprestore/includes/class-wpvivid-mysqldump-method.php), task id: wpvivid-…..5d965, Please switch to Website Info page to send us the debug information.”