An invoice letter is a simple cover letter that goes with a formal invoice to a company that owes money on a bill. An invoice letter created in Invoices is sent to customers. For more information, see Creating an invoice letter.

Freezing invoice: Once the invoice has been reviewed, approved, and considered final, it can be frozen. Freezing means that no further changes or edits can be made to the invoice data. It is essentially locked to prevent accidental or unauthorized alterations. After freezing an invoice, it is typically ready for payment. The freezing process ensures that the financial data associated with the invoice remains consistent and accurate throughout the payment process.