You may need to have multiple folios in an invoice to split the different types of charges for a guest.
You can add a folio to an invoice by opening the invoice of the reservation you want to add the invoice to and clicking the Add Folio button.
Once you click that button a folio will be added to the invoice. Just click on the tab that shows the newly added folio and you can start using it in the same way as you were using the single folio.
You can have a maximum of 10 folios in a reservation, they function independently of each other, and you can transfer any transactions between them.