WHY
If you have a retainer Project for a client and you are billing him on fixed dates month after month, you can create a Recurring Budget in Productive. A new Budget will be created month after month (or in a different interval, depending on your choice) and you will be warned that you should Invoice your client automatically.
WHERE
Go to your Budget and click on the Recurring tab.
HOW
Click on the Make this a recurring budget button.