Hi BANCO,
The system doesn't automatically alert you about existing credit notes when creating a new invoice. However, you can manually check for available credits by going to the customer's record before issuing a new invoice. When applying payments, you'll also have the option to use the credit note against the outstanding balance. You can refer to this link: Customer returns, credits and refunds.
If having an automatic notification for credit notes when creating invoices would be useful for your workflow, we recommend submitting this idea to the Ideas Board. We actively review customer suggestions to improve the software, and your feedback could help shape future updates.
Regards,
Sai