I appreciate you following the instruction shared by my colleague above, Sharon.

At this time, QuickBooks only allows you to send a payment reminder to your customers once. That's why you received an error that you need to create a new schedule.

I know that sending a follow-up reminder to your customer that hasn't paid yet can help save your time, instead of creating a new scheduled reminder every month. For now, I suggest submitting feedback directly to our product engineers. This way, they can review your request and add it to the future update. To submit feedback, you can go to the Help menu and select Send Feedback Online. Then, choose Product Suggestions and enter your feedback.

You may want to run and customize a report to view all your sales transactions in QuickBooks Desktop. This article will help you through the steps: Customize reports in QuickBooks Desktop.

Our Community forum is always open to help you again if you need further assistance on this concern. Have a good one.