**Reference one invoice to an expense**

* Create an expense sheet.
* Add an expense line to sheet with an invoice_id selected or create one new.
* Process expense sheet.
* On paying expense sheet, you are reconciling supplier invoice too.

**Create one invoice to multiple expenses**

* Create an expense sheet with one or multiple expense lines
* After approved, click button "Create Vendor Bill"
* Select multiple expense to create an invoice, and process it.
* New invoice will be create and link to the selected expense lines.
* Validate newly create invoice.
* On paying expense sheet, you are reconciling supplier invoice(s) too.
