Create first customer invoice and register payment

Users can also create invoices manually without using contracts or a sales order. It's a recommended approach if you do not need to manage the sales process (quotations), or the delivery of the products or services.

Even if you generate the invoice from a sales order, you may need to create invoices manually in exceptional use cases:

if you need to create a refund
If you need to give a discount
if you need to change an invoice created from a sales order
if you need to invoice something not related to your core business