User has some old invoices that the client will no longer pay. So the user wants to issue a credit note to the client by creating a credit memo of type Project Credit and wants to know if it will add the balance to the overall amount due.
If you use a credit memo for this purpose, it won't affect the overall amount due (Accounts Receivable), but rather it will increase your liability (Accounts Payable) as the credit memos in Core are used to pay back project credits or refund retainers. Check the Core Help for details.
To handle this properly, you should instead use a payment of type Credit or Write-Off on the invoices in the Payments screen. These will reduce the A/R and also register as an expense on the accounting side. Check the Core Help for details on credit payments and write-off.
You can print or email a receipt to the client for reference from the Payments screen by selecting the payment and clicking on More > View Reports. Use the Payment Receipt report for write-offs and the Credit Payment Receipt report for credit payments. You can also do this with more flexibility from the Reports screen by selecting these reports under Payments and using the appropriate filters and options.