Final invoice represents an invoice created form advance payment invoice. Advance payment invoice is used as a conformation for received payments for the products or goods that still haven't been delivered. Upon delivery of goods and services, for which advance payment invoice was created, a final invoice is created form advance payment invoice. Final invoice, along with delivered product and services, includes deduction of the amount payed in advance.
In order to create the Final invoice from the advance payment invoice, click on the Create final invoice option from the invoice details menu. 
The option is available only for the approved Advance payment invoices.
When the Final invoice is created, the date of the invoice is set to current date. Some data that is copied from the original invoice:
- Basic information - partner, category, currency, TAX included, department, payment method.
- Invoice items - items and quantities are copied but in negative quantities.
Add services and/or goods to the final invoice  and specify the quantity, unit price, and discount for each. 
The total amount will be calculated automatically taking into consideration the registered advanced payment.
Link to the advance payment invoice is visible at the bottom of the invoice Details/Edit page.
Create final invoice from more than one advanced payment
You can create final invoice from more than one advanced payment, click on the Create final invoice option from the bulk options menu. 
Select invoices  from the list, and then click on the [Create final invoice] button. 
In order to create Final invoice from more than one Advance payment invoice, the Advance payment invoices should have same values for the following fields: