Thanks for the immediate response, @cmeisel. Let me further guide you in adding payment terms for your invoices in QuickBooks Online (QBO).

You're already on the right track when adding terms or agreements between you and your customers regarding when their invoice payments are due in QBO. To add a new one, you can indicate the Due in a fixed number of days, Due by a certain day of the month, and Due the next month if issued within days of the due date. 

For example, when you've created an invoice on the 1st day of the month (July 1, 2022) and its payment is due by the 30th day of the same month (July 30, 2022), you can either select the Due in a fixed number of days or Due by certain day of the month option and then enter 30 in the day or day of the month box. Please see the screenshot below for your reference.

You can learn more about adjusting invoice terms by checking out this article: How to adjust Invoice Payment Terms in QuickBooks Online.

Once your invoices are sent, you can pull up the Terms QuickReport to monitor your transactions. You can do this by going to the Gear icon and selecting All lists. From there, choose Terms to display the list of terms you have and click the Run report option.

Also, you may want to check out this article as your reference in case you need to set up and add late fees to overdue invoices in QBOI: Set up and apply automatic late fees to invoices.

Let me know if you have other concerns about payment terms or questions about managing invoices and income transactions in QBO. I'm always ready to help. Take care, and have a great day, @cmeisel.