You can set up an email to automatically remind your clients when they have a balance due on a booking.
Go to Manage --> Automated Messages.
Click the New Automated Message button
Select the Payment Due Date email template group.
Select one of the pre-made templates or create your own.
Customize the message template and click Save.
Note that if you choose to add conditions, ALL the conditions must all be met in order for the automated email to trigger.
For messages that are scheduled to go out X Days before or after, the scheduled sending time is approximately 11 AM local time.