Why do invoices appear as paid automatically without adding a payment?

This happens when the “Auto Pay Invoices if the Client Has Available Credit” option is enabled. You can find it under “Sales” > “Sales Settings” > “Invoices & Estimates Settings.”

When this option is activated, the system automatically checks the client’s account for any previous payments or credit notes and applies them to the new invoice, marking it as paid.

Note: Refer to this guide for more details on the “Auto Pay Invoices if the Client Has Available Credit” guide.