When can an Invoice be created?

The correct time and way for creating an Invoice is at any point after the Fulfillment Order is created, by customizing flow “Create Invoice”. This flow is a core action that creates an Invoice record from a Fulfillment Order record, and updates the status of both records accordingly. The administrator can customize this flow to suit their business needs,such as adding conditions, actions, or subflows. Verified References:https://help.salesforce.com/s/articleView?id=sf.flow_ref_elements_ om_actions_create_invoice.htm&type=5