Summary:
If you make changes to a booked event after all originally scheduled payments have been made, then you need to manually add a new payment and set it to the value of the latest changes.
Instructions:
Unlock the event by clicking the lock icon (top right) and go to Payments tab
Add up the payments already received, take note of this number
Then take the Price number on the Event Card at the top, and subtract the total of payments already received. Take note of the difference.
Click "ADD SCHEDULED PAYMENT" and set the payment type to $ and set the amount to the difference of the Price on the Event Card at the top, and the sum of the payments already received.
Set the due date to be in the future