Access your Settings page, and click the Feeds tab.
You will find a URL there for the "Cron Job". Create a cron job with the following settings:
0 10 * * * wget -O /dev/null -q http://example.com/index.php/cron/invoices/<unique-code>
Replacing the URL with the "Cron Job" URL you saw in your Settings page.
That's it! If you've done everything correctly, your cron job should be working now.
WARNING: If you're running your Pancake with HTTPS, and your wget is not configured correctly on your server, you may have problems loading the site with wget. If that's the case, you can add --no-check-certificate just after -q, and the problem should go away.
If you have no experience with setting up cron jobs on servers or don't have access to do it, you can use a third party solution like EasyCron (Free) or SetCronJob (Paid) who will call your URL at a specific time.
If you have any problems setting up your cron job, let us know by starting a free support ticket.