Good Afternoon,
The Simple Invoice report is designed to display all outstanding invoices for your customers. If you can let me know for what reason are you looking at filtering the invoices, perhaps I can provide some guidance. For instance, If you are looking to filter the invoices by a certain dollar amount (let’s say greater than or equal to zero to reflect those with outstanding balances), then you would click Edit on the Report object itself in the design screen to edit the report’s properties. Step 2 of the wizard will allow you to change the filter options.
Have a great weekend! 