You can transfer an open invoice to cash transaction so then it can be paid in cash or by card.

First, open an open invoice that you want to transfer to the cash transaction. Click the Take to POS -button (at the bottom of the Invoice page) to start the invoice transfer to the cash register. 

Next, the software asks for confirmation of the invoice transfer to the cash register. The transferred invoice will be removed from the billing during the transfer. Click the Transfer to Cash Register -button to continue the transfer.

Next the software opens a cash view where the transferred event is ready. You can edit, add or remove products from the cash transaction. Finally, the transaction can be decided using the Cash Payment or Card Payment -button as a normal cash transaction.