AI, which isn't guaranteed 100% accurate, has this to offer...
"The duplicate payment showing on the invoice statement in NCH Express Invoice (Windows v.946) despite no visible double payments or credit notes is a known issue sometimes caused by the software misapplying or duplicating payment entries internally even after deleting payments or recalculating balances.
To resolve this:
Verify all payments linked to the customer and invoice in the Payments window and delete any duplicates from there.
Check that there are no credit notes or unapplied credits linked to the customer that might be causing the duplicate sum to reflect.
Confirm the customer balance was recalculated after removing any duplicate or incorrect payments.
If the issue persists, exporting customer info, uninstalling and reinstalling Express Invoice, then re-importing the customer data can clear hidden duplicates or corruption.
Also, verify the system date format settings in Windows (in Control Panel under Region and Language) are consistent, as odd formats can cause misreads in payment application.
Contact NCH support if none of the above resolves the issue as it suggests a deeper bug or data corruption in the invoice database.
Following these steps should clear false duplicate payment displays and balance issues in Express Invoice v.946 on Windows, according to user reports and official advice from NCH forums and knowledge base."