register-payment
Use when the task says the customer ALREADY HAS an unpaid invoice and asks to register/record the payment. Keywords: 'facture impayée', 'unbezahlte Rechnung', 'ubetalt faktura', 'unpaid invoice', 'fatura pendente'. The invoice ALREADY EXISTS — do NOT create a new one. If the task mentions creating products, orders, or new invoices, use order_invoice_payment instead.