Hi there stillkat-gmail-c,
It's vital that you're able to keep track of payments made by your customers. QuickBooks Online offers a variety of reports to help you visualize certain parts of the financials of your business. I can point you in the right direction for a report that shows you the payments made by your customers.
A report that shows you the payments made by a customer would be the Invoices and received payments report. It shows you the payments you've received as well as which invoices are associated with it. You can find the report by navigating to the Reports tab and scrolling down to the Who owes you section. You can also use the steps in the article provided by SelenaN to help you customize this report.
If you have any other questions, feel free to reach out here.