In order to setup reoccuring invoices, you need to add a cron job to your site. We recommend having the cron execute once per day. The following cron settings need to be applied:
0 * * * * * wget
The cron job will then execute once every day (usually at midnight) and generate the reoccuring invoices if any are available. Make sure you have invoices to be generated by setting them up in the Reoccuring Invoices section of the system.
If you're using cPanel, this guide may be helpful in setting up a cron job.