Hi Karen,
You're talking about 'Customers' so I assume you're looking for historical Sales transactions, posted invoiced and applied payments to the invoices..
You should take a look at the customer statements, as this will print you a report with historical & open invoices, plus all the applied payments, and the outstanding amounts.
Sales >> Routines >> Statements
See from the help:
Use the Print Receivables Statements window to set up and print customer statements. You should assess finance charges, enter and post transactions, enter and post payments, and age customer accounts before printing statements using this window. See Aging customer accounts and Assessing finance charges for more information.
To print statements only for customers with monthly statement cycles, choose by Statement Cycle from the Ranges sort-by list and select from Monthly to Monthly for the range of statement cycles. To set up a special statement form customized to meet your business' needs, modify the default statement form using Report Writer.
You can even e-mail the statements to the customers on a monthly basis or as requested.
SOP Invoices can be reprinted any time for the customers, and there are some valuable SQL views that you can use for free from Victoria Yudin to build some Excel reports or SmartLists (if you're licensed for SMartList Designer or own SmartList Builder from eOne).
https://victoriayudin.com/gp-reports/receivables-sql-views/