Greetings, @chris99!

Let's pull up and customize your Transaction List by Customer report so you can identify how many days your customers pay their invoices.

1. Go to Report's
2. Select Standard.
3. Scroll down the page to Sales and customers category of your reports.
4. Choose Transaction List by Customer.
5. Click Customise.
6. Under Filter, select Transaction Type.
7. On the Transaction Type menu, select Invoice and Payment.
8. Click Run Report.

In addition, here's a couple of screenshots for your visual reference and an article you can read to learn more about customizing your report: How to Customise Reports?

Lastly, you can also save this customized report by clicking Save customisation. This way, you can easily pull up this report when needed in the future. You can find this report in your Custom reports tab.

If there's anything else that I can help you with, please let me know in the comment section down below. I'll be always around ready to help.