Which object is used to createan invoice?

The Order Summary object is used to create an invoice. An invoice is a document that requests payment from a customer for an order. An invoice can include one or more fulfillment orders and one or more credit memos. A fulfillment order is a record that represents a part of an order that is fulfilled by a specific location. A credit memo is a record that represents a partial or full refund for an order or a fulfillment order. To create an invoice, an administrator can use the Create Invoice Apex action in a flow. The Create Invoice Apex action requires the Order Summary ID as an input parameter and creates an Invoice record associated with the Order Summary record. References: Order Management Objects, [Create Invoice Apex Action]