If you're looking to give your guest a receipt, then try using the Print button on a booking page.
You'll only want to use this to invoice your guest to pay for their reservation at a later date - using Invoice Guest is a way to bypass recording charges for a booking. Preno sees the invoice as a payment for the booking, but you'll need to record any payment outside of Preno.
Creating the invoice
You can either find the booking on the grid, or by searching for it on the Bookings page. Click on the reservation that you'd like to invoice, and click Add Payment.
From the payment method dropdown select Invoice guest
Check you have the correct amount and guest name then click Add.
Scroll down the page to the Charges and Payments section, the second column along should read type, below that will be a clickable link that says Invoice guest.
When you click on it, Preno will download a .PDF invoice to your computer. If you use the Xero integration, a draft invoice will be created in Xero.
Invoicing with the Xero integration:
If you have the Xero integration enabled, Preno will create a draft invoice in Xero. You'll need to manually approve the invoice, and record payments on it.
Remember, Preno automatically creates an invoice for the guest on check out if you record charges on the booking.