The Invoices feature is available in the Sales Pack extension.
An Invoice is a billing document issued to a customer that details the products or services provided, including their quantities, prices, applicable taxes, and the total amount due. It serves as a bill for the customer and is usually sent before shipping the goods or providing the services. As a rule, an invoice contains the list of items (namely products and services) that must be paid for, their quantity, price, taxes, discount rates, delivery details, and payment terms.
In EspoCRM, invoices can be either manually created by users or automatically generated from the quote, sales order or opportunity records.
An invoice’s outstanding amount can be settled through the allocation of inbound payments or credit notes.
Invoices can be printed to PDF. You are able to create multiple custom templates, which include your custom fields and fit your company design. An invoice PDF can be send in email to a customer.

Debit notes
An invoice can be issued as a debit note. Debit notes are useful when the outstanding amount needs to be increased without issuing a new invoice. An invoice record issued as a debit note uses separate numbering.
E-Invoices
An invoice can be exported to EN 16931 electronic invoice in a UBL format.
Documentation
For more detail information on the Invoices feature, see documentation.