Cron deamon message

Since a few months I am getting this email with the message:

Subject: Cron /opt/php70/bin/php -d memory-limit=2048M /home/httpd/vhosts/ > /dev/null

The message is:

PHP Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 10489856 bytes) in /home/httpd/vhosts/blabla/httpdocs/owncloud/apps/ownbackup/service/backupservice.php on line 92

I am running Nextcloud (was first on owncloud) on a shared server.

can someone help?