By utilizing Invoice Templates and our Workflows, you can automatically send invoices to your clients at the right time - and avoid late payments.
First create an invoice template (see Invoice Template instructions here).
Once you've created your invoice, you will want to attach it to an email message. Customize your email (via Email Templates), and attach your invoice, and any other items you wish to attach, at the bottom of the page.
Finally, visit your Workflows tab in your Profile. Select 'Scheduled Email', and then select your Invoice Email from the drop down list. Now you can choose when you wish the email (and invoice) to be sent.